Form 485BPOS VANGUARD ADMIRAL FUNDS

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

VANGUARD ADMIRAL FUNDS

(Exact Name of Registrant as Specified in Declaration of Trust)

P.O. Box 2600, Valley Forge, PA 19482

(Address of Principal Executive Office)

Registrant’s Telephone Number (610) 669-1000

Anne E. Robinson, Esquire

P.O. Box 876

Valley Forge, PA 19482

Vanguard Money Market Funds Prospectus

December 20, 2018

Investor Shares

Vanguard Prime Money Market Fund Investor Shares (VMMXX) Vanguard Federal Money Market Fund Investor Shares (VMFXX) Vanguard Treasury Money Market Fund Investor Shares (VUSXX)

This prospectus contains financial data for the Funds through the fiscal year ended August 31, 2018.

The Securities and Exchange Commission (SEC) has not approved or disapproved these securities or passed upon the adequacy of this prospectus. Any representation to the contrary is a criminal offense.

Vanguard Prime Money Market Fund

Investment Objective

The Fund seeks to provide current income while maintaining liquidity and a stable share price of $1.

Fees and Expenses

The following table describes the fees and expenses you may pay if you buy and hold Investor Shares of the Fund.

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Example

The following example is intended to help you compare the cost of investing in the Fund’s Investor Shares with the cost of investing in other mutual funds. It illustrates the hypothetical expenses that you would incur over various periods if you were to invest $10,000 in the Fund’s shares. This example assumes that the shares provide a return of 5% each year and that total annual fund operating expenses remain as stated in the preceding table. You would incur these hypothetical expenses whether or not you redeem your investment at the end of the given period. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Principal Investment Strategies

The Fund invests primarily in high-quality, short-term money market instruments, including certificates of deposit, banker’s acceptances, commercial paper, Eurodollar and Yankee obligations, and other money market securities. To be considered high quality, a security must be determined by Vanguard to present minimal credit risk based in part on a consideration of maturity, portfolio diversification, portfolio liquidity, and credit quality. The Fund invests more than 25% of its assets in securities issued by companies in the financial services industry. The Fund maintains a dollar-weighted average maturity of 60 days or less and a dollar-weighted average life of 120 days or less.

Principal Risks

The Fund is designed for investors with a low tolerance for risk; however, the Fund is subject to the following risks, which could affect the Fund’s performance:

• Income risk, which is the chance that the Fund’s income will decline because of falling interest rates. Because the Fund’s income is based on short-term interest rates—which can fluctuate significantly over short periods—income risk is expected to be high.

• Manager risk, which is the chance that poor security selection will cause the Fund to underperform relevant benchmarks or other funds with a similar investment objective.

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• Credit risk, which is the chance that the issuer of a security will fail to pay interest or principal in a timely manner or that negative perceptions of the issuer’s ability to make such payments will cause the price of that security to decline. Credit risk should be very low for the Fund because it invests primarily in securities that are considered to be of high quality.

• Industry concentration risk, which is the chance that there will be overall problems affecting a particular industry. Because the Fund invests more than 25% of its assets in securities issued by companies in the financial services industry, the Fund’s performance depends to a greater extent on the overall condition of that industry and is more susceptible to events affecting that industry.

You could lose money by investing in the Fund. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. The Fund may impose a fee upon sale of your shares or may temporarily suspend your ability to sell shares if the Fund’s liquidity falls below required minimums because of market conditions or other factors. An investment in the Fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The Fund’s sponsor has no legal obligation to provide financial support to the Fund, and you should not expect that the sponsor will provide financial support to the Fund at any time.

Annual Total Returns

The following bar chart and table are intended to help you understand the risks of investing in the Fund. The bar chart shows how the performance of the Fund‘s Investor Shares has varied from one calendar year to another over the periods shown. The table shows how the average annual total returns of the Investor Shares compare with those of a relevant market index and a comparative benchmark, which have investment characteristics similar to those of the Fund. Returns for the Money Market Funds Average are derived from data provided by Lipper, a Thomson Reuters Company. Keep in mind that the Fund’s past performance does not indicate how the Fund will perform in the future. Updated performance information is available on our website at vanguard.com/performance or by calling Vanguard toll-free at 800-662-7447.

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Annual Total Returns — Vanguard Prime Money Market Fund Investor Shares¹

1 The year-to-date return as of the most recent calendar quarter, which ended on September 30, 2018, was 1.37%.

During the periods shown in the bar chart, the highest return for a calendar quarter was 0.96% (quarter ended March 31, 2008), and the lowest return for a quarter was 0.00% (quarter ended March 31, 2014).

Investment Advisor

The Vanguard Group, Inc. (Vanguard)

Portfolio Manager

Nafis T. Smith, Portfolio Manager at Vanguard. He has managed the Fund since 2017.

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Purchase and Sale of Fund Shares

You may purchase or redeem shares online through our website (vanguard.com), by mail (The Vanguard Group, P.O. Box 1110, Valley Forge, PA 19482-1110), or by telephone (800-662-2739). When your trade is processed depends on the day and time Vanguard receives your request in good order and the manner in which it is submitted. Generally, trades placed after the close of business are processed during the next business day. The minimum investment amount required to open and maintain a Fund account for Investor Shares is $3,000. The minimum investment amount required to add to an existing Fund account is generally $1. Financial intermediaries and Vanguard-advised clients should contact Vanguard for special eligibility rules that may apply to them regarding Investor Shares. If you are investing through an intermediary, please contact that firm directly for more information regarding your eligibility. The Fund is only available for purchase within accounts beneficially owned by natural persons. If you are investing through an employer-sponsored retirement or savings plan, your plan administrator or your benefits office can provide you with detailed information on how you can invest through your plan.

Tax Information

The Fund’s distributions may be taxable as ordinary income or capital gain. If you are investing through a tax-advantaged account, such as an IRA or an employer-sponsored retirement or savings plan, special tax rules apply.

Payments to Financial Intermediaries

The Fund and its investment advisor do not pay financial intermediaries for sales of Fund shares.

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Vanguard Federal Money Market Fund

Investment Objective

The Fund seeks to provide current income while maintaining liquidity and a stable share price of $1.

Fees and Expenses

The following table describes the fees and expenses you may pay if you buy and hold shares of the Fund.

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Example

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. It illustrates the hypothetical expenses that you would incur over various periods if you were to invest $10,000 in the Fund’s shares. This example assumes that the Fund provides a return of 5% each year and that total annual fund operating expenses remain as stated in the preceding table. You would incur these hypothetical expenses whether or not you redeem your investment at the end of the given period. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Principal Investment Strategies

The Fund invests primarily in high-quality, short-term money market instruments. Under normal circumstances, at least 80% of the Fund’s assets are invested in securities issued by the U.S. government and its agencies and instrumentalities. Although these securities are high-quality, most of the securities held by the Fund are neither guaranteed by the U.S. Treasury nor supported by the full faith and credit of the U.S. government. To be considered high quality, a security must be determined by Vanguard to present minimal credit risk based in part on a consideration of maturity, portfolio diversification, portfolio liquidity, and credit quality. The Fund maintains a dollar-weighted average maturity of 60 days or less and a dollar-weighted average life of 120 days or less.

Under the recent money market reforms, government money market funds are required to invest at least 99.5% of their total assets in cash, government securities, and/or repurchase agreements that are collateralized solely by government securities or cash (collectively, government securities). The Fund generally invests 100% of its assets in government securities and therefore will satisfy the 99.5% requirement for designation as a government money market fund.

Principal Risks

The Fund is designed for investors with a low tolerance for risk; however, the Fund is subject to the following risks, which could affect the Fund’s performance:

• Income risk, which is the chance that the Fund’s income will decline because of falling interest rates. Because the Fund’s income is based on short-term interest rates—which can fluctuate significantly over short periods—income risk is expected to be high.

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• Manager risk, which is the chance that poor security selection will cause the Fund to underperform relevant benchmarks or other funds with a similar investment objective.

• Credit risk, which is the chance that the issuer of a security will fail to pay interest or principal in a timely manner or that negative perceptions of the issuer’s ability to make such payments will cause the price of that security to decline. Credit risk should be very low for the Fund because it invests primarily in securities that are considered to be of high quality.

You could lose money by investing in the Fund. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. An investment in the Fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The Fund’s sponsor has no legal obligation to provide financial support to the Fund, and you should not expect that the sponsor will provide financial support to the Fund at any time.

Annual Total Returns

The following bar chart and table are intended to help you understand the risks of investing in the Fund. The bar chart shows how the performance of the Fund has varied from one calendar year to another over the periods shown. The table shows how the average annual total returns of the Fund compare with those of a relevant market index and a comparative benchmark, which have investment characteristics similar to those of the Fund. Returns for the U.S. Government Money Market Funds Average are derived from data provided by Lipper, a Thomson Reuters Company. Keep in mind that the Fund’s past performance does not indicate how the Fund will perform in the future. Updated performance information is available on our website at vanguard.com/performance or by calling Vanguard toll-free at 800-662-7447.

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Annual Total Returns — Vanguard Federal Money Market Fund Investor Shares¹

1 The year-to-date return as of the most recent calendar quarter, which ended on September 30, 2018, was 1.23%.

During the periods shown in the bar chart, the highest return for a calendar quarter was 0.94% (quarter ended March 31, 2008), and the lowest return for a quarter was 0.00% (quarter ended March 31, 2014).

Average Annual Total Returns for Periods Ended December 31, 2017

Investment Advisor

The Vanguard Group, Inc. (Vanguard)

Portfolio Manager

John C. Lanius, Portfolio Manager at Vanguard. He has managed the Fund since 2007.

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Purchase and Sale of Fund Shares

You may purchase or redeem shares online through our website (vanguard.com), by mail (The Vanguard Group, P.O. Box 1110, Valley Forge, PA 19482-1110), or by telephone (800-662-2739). When your trade is processed depends on the day and time Vanguard receives your request in good order and the manner in which it is submitted. Generally, trades placed after the close of business are processed during the next business day. The minimum investment amount required to open and maintain a Fund account for Investor Shares is $3,000. The minimum investment amount required to add to an existing Fund account is generally $1. Financial intermediaries, institutional, and Vanguard-advised clients should contact Vanguard for information on special eligibility rules that may apply to them regarding Investor Shares. If you are investing through an intermediary, please contact that firm directly for more information regarding your eligibility. If you are investing through an employer-sponsored retirement or savings plan, your plan administrator or your benefits office can provide you with detailed information on how you can invest through your plan.

Tax Information

The Fund’s distributions may be taxable as ordinary income or capital gain. If you are investing through a tax-advantaged account, such as an IRA or an employer-sponsored retirement or savings plan, special tax rules apply.

Payments to Financial Intermediaries

The Fund and its investment advisor do not pay financial intermediaries for sales of Fund shares.

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Vanguard Treasury Money Market Fund

Investment Objective

The Fund seeks to provide current income while maintaining liquidity and a stable share price of $1.

Fees and Expenses

The following table describes the fees and expenses you may pay if you buy and hold shares of the Fund.

The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. It illustrates the hypothetical expenses that you would incur over various periods if you were to invest $10,000 in the Fund’s shares. This example assumes that the Fund provides a return of 5% each year and that total annual fund operating expenses remain as stated in the preceding table. You would incur these hypothetical expenses whether or not you redeem your investment at the end of the given period. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

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Principal Investment Strategies

The Fund invests solely in high-quality, short-term money market securities whose interest and principal payments are backed by the full faith and credit of the U.S. government. Under normal circumstances, at least 80% of the Fund’s assets will be invested in U.S. Treasury securities; the remainder of the assets may be invested in securities issued by U.S. governmental agencies. The Fund maintains a dollar-weighted average maturity of 60 days or less and a dollar-weighted average life of 120 days or less.

Under the recent money market reforms, government money market funds are required to invest at least 99.5% of their total assets in cash, government securities, and/or repurchase agreements that are collateralized solely by government securities or cash (collectively, government securities). The Fund generally invests 100% of its assets in government securities and therefore will satisfy the 99.5% requirement for designation as a government money market fund.

Principal Risks

The Fund is designed for investors with a low tolerance for risk; however, the Fund is subject to the following risks, which could affect the Fund’s performance:

• Income risk, which is the chance that the Fund’s income will decline because of falling interest rates. Because the Fund’s income is based on short-term interest rates—which can fluctuate significantly over short periods—income risk is expected to be high.

• Manager risk, which is the chance that poor security selection will cause the Fund to underperform relevant benchmarks or other funds with a similar investment objective.

You could lose money by investing in the Fund. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. An investment in the Fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The Fund’s sponsor has no legal obligation to provide financial support to the Fund, and you should not expect that the sponsor will provide financial support to the Fund at any time.

Annual Total Returns

The following bar chart and table are intended to help you understand the risks of investing in the Fund. The bar chart shows how the performance of the Fund has varied from one calendar year to another over the periods shown. The table shows how the average annual total returns of the Fund compare with those of a relevant market index and a comparative benchmark, which have investment characteristics similar to those of the Fund. Returns for the iMoneyNet Money Fund Report‘s 100%

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Treasury Funds Average are derived from data provided by iMoneyNet, Inc.; returns for the U.S. Treasury Money Market Funds Average are derived from data provided by Lipper, a Thomson Reuters Company. Keep in mind that the Fund’s past performance does not indicate how the Fund will perform in the future. Updated performance information is available on our website at vanguard.com/performance or by calling Vanguard toll-free at 800-662-7447.

Annual Total Returns — Vanguard Treasury Money Market Fund Investor Shares¹

1 The year-to-date return as of the most recent calendar quarter, which ended on September 30, 2018, was 1.25%.

During the periods shown in the bar chart, the highest return for a calendar quarter was 0.81% (quarter ended March 31, 2008), and the lowest return for a quarter was 0.00% (quarter ended March 31, 2015).

Average Annual Total Returns for Periods Ended December 31, 2017

Investment Advisor

The Vanguard Group, Inc. (Vanguard)

Portfolio Manager

Nafis T. Smith, Portfolio Manager at Vanguard. He has managed the Fund since 2017.

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Purchase and Sale of Fund Shares

You may purchase or redeem shares online through our website (vanguard.com), by mail (The Vanguard Group, P.O. Box 1110, Valley Forge, PA 19482-1110), or by telephone (800-662-2739). When your trade is processed depends on the day and time Vanguard receives your request in good order and the manner in which it is submitted. Generally, trades placed after the close of business are processed during the next business day. The minimum investment amount required to open and maintain a Fund account for Investor Shares is $50,000. The minimum investment amount required to add to an existing Fund account is generally $1. Financial intermediaries, institutional, and Vanguard-advised clients should contact Vanguard for information on special eligibility rules that may apply to them regarding Investor Shares. If you are investing through an intermediary, please contact that firm directly for more information regarding your eligibility. If you are investing through an employer-sponsored retirement or savings plan, your plan administrator or your benefits office can provide you with detailed information on how you can invest through your plan.

Tax Information

The Fund’s distributions may be taxable as ordinary income or capital gain. If you are investing through a tax-advantaged account, such as an IRA or an employer-sponsored retirement or savings plan, special tax rules apply.

Payments to Financial Intermediaries

The Fund and its investment advisor do not pay financial intermediaries for sales of Fund shares.

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Investing in Money Market Funds

What is Money Market Reform?

In July 2014, the Securities and Exchange Commission (SEC) implemented a number of regulatory changes designed to enhance the stability and resilience of all money market funds. The reforms have created three categories of money market funds:

• Retail money market funds, which may maintain a stable net asset value (NAV) but are subject to liquidity fees and redemption gates.

• Government money market funds, which may maintain a stable NAV but are not required to implement liquidity fees and redemption gates.

• Institutional money market funds, which are required to have a floating NAV and are subject to liquidity fees and redemption gates.

The boards of trustees of Vanguard Money Market Reserves and Vanguard Admiral Funds^® (collectively, the Boards), in accordance with the best interest of the shareholders, approved a number of changes in response to the SEC’s 2014 amendments to the rules governing money market funds. These changes—including the Board’s ability to implement liquidity fees and redemption gates if Vanguard Prime Money Market Fund’s weekly liquid assets fall below established thresholds—are now in effect. As part of these changes, information regarding each Fund’s weekly liquid assets for the prior six months (by day, as of the close of business) is available on each Fund’s Portfolio page at vanguard.com.

How Does This Affect Vanguard Money Market Funds?

The money market fund reforms impact money market funds differently depending on the types of investors permitted to invest in a fund and the types of securities in which a fund may invest.

Vanguard Prime Money Market Fund

Vanguard has designated Vanguard Prime Money Market Fund as a retail money market fund.

Retail money market funds are defined as prime or tax-exempt money market funds that have policies and procedures reasonably designed to limit all beneficial owners of such money market funds to natural persons. Retail money market funds are permitted to continue to maintain a stable NAV through the use of amortized cost accounting. If a retail money market fund’s weekly liquid assets fall below a certain threshold, the retail money market fund is subject to fees and gates.

There are two types of liquidity fees: discretionary liquidity fees and default liquidity fees. Liquidity fees are designed to transfer the costs of liquidating securities from shareholders who remain in the Fund to those who leave the Fund during periods when liquidity is limited.

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Discretionary liquidity fee. The Fund may impose a liquidity fee of up to 2% on all redemptions in the event that the Fund’s weekly liquid assets fall below 30% of its total assets if the Board determines that it is in the best interest of the Fund. Subject to practical limitations necessary to implement the fee, the discretionary liquidity fee may be implemented the same day that the Board determines to impose a fee. Once the Fund has restored its weekly liquid assets to 30% of total assets, any liquidity fee must be suspended.

Default liquidity fee. The Fund is required to impose a liquidity fee of 1% on all redemptions in the event that the Fund’s weekly liquid assets fall below 10% of its total assets unless the Fund’s Board determines that (1) the fee is not in the best interest of the Fund or (2) a lesser/higher fee (up to 2%) is in the best interest of the Fund. A default liquidity fee is required to be implemented the business day after the Board determines to impose a fee.

In addition to, or in lieu of, the liquidity fee, the Fund is permitted to temporarily implement a redemption gate (i.e., suspend redemptions) if the Fund’s weekly liquid assets fall below 30% of its total assets. The gate could remain in effect for no longer than 10 days in any 90-day period. Once the Fund has restored its weekly liquid assets to 30% of total assets, the gate must be lifted.

Once the Fund imposes a redemption gate, then unprocessed orders to redeem or exchange will be canceled and the Fund will not accept redemption or exchange orders until the gate is no longer in effect. If you still wish to redeem or exchange once the gate is lifted, you will need to submit a new redemption or exchange request to the Fund or your financial intermediary.

The Board also may determine that it would not be in the interests of the Fund to continue operating if the Fund’s weekly liquid assets fall below 10% of its total assets. In the event that the Board approves liquidation of the Fund under these circumstances, the Fund may permanently suspend redemptions and liquidate.

Notices regarding liquidity fees or redemption gates will be filed with the SEC on Form N-CR. In addition, announcements will also be made in supplements to the Fund’s prospectus and on the Fund’s website.

Vanguard Federal Money Market Fund and Vanguard Treasury Money Market Fund

Vanguard has designated Vanguard Federal Money Market Fund and Vanguard Treasury Money Market Fund as government money market funds.

Under the recent money market reforms, government money market funds are required to invest at least 99.5% of their total assets in cash, government securities,

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and/or repurchase agreements that are collateralized solely by government securities or cash (collectively, government securities). Both Funds generally invest 100% of their assets in government securities and therefore will satisfy the 99.5% requirement for designation as a government money market fund.

Government money market funds can also maintain a stable $1.00 NAV through the use of amortized cost accounting and may, but are not required to, implement liquidity fees and redemption gates. Both Funds will continue to use amortized cost to transact at a stable $1.00 NAV.

The Boards have determined that the Vanguard government money market funds will not voluntarily implement the new liquidity fees or redemption gates.

Each Fund is subject to money market fund reform regulatory risk, which is the chance that 2014 SEC reforms will affect the Fund’s investment strategy, fees and expenses, portfolio, share liquidity, and return potential as a result of the implemented rules.

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More on the Funds

This prospectus describes the principal risks you would face as a Fund shareholder. It is important to keep in mind one of the main principles of investing: generally, the higher the risk of losing money, the higher the potential reward. The reverse, also, is generally true: the lower the risk, the lower the potential reward. As you consider an investment in any mutual fund, you should take into account your personal tolerance for fluctuations in the securities markets. Look for this symbol throughout the prospectus. It is used to mark detailed information about the more significant risks that you would confront as a Fund shareholder. To highlight terms and concepts important to mutual fund investors, we have provided Plain Talk® explanations along the way. Reading the prospectus will help you decide whether a Fund is the right investment for you. We suggest that you keep this prospectus for future reference.

Share Class Overview

This prospectus offers the Funds‘ Investor Shares. A separate prospectus offers Admiral^TM Shares of Vanguard Prime Money Market Fund. Admiral Shares are generally for investors who invest a minimum of $5 million.

Both share classes offered by the Prime Money Market Fund have the same investment objective, strategies, and policies. However, different share classes have different expenses; as a result, their investment returns will differ.

The following sections explain the principal investment strategies and policies that each Fund uses in pursuit of its objective. The Funds’ board of trustees, which oversees each Fund’s management, may change investment strategies or policies in the interest of shareholders without a shareholder vote, unless those strategies or policies are designated as fundamental. The Federal Money Market Fund and the Treasury Money Market Fund each generally invest 100% of their assets in government securities and therefore will satisfy the 99.5% requirement for designation as a government money market fund. The Federal Money Market Fund’s policy and the Treasury Money Market Fund’s policy of investing at least 99.5% of assets in government securities may be changed only upon 60 days’ notice to shareholders. The Federal Money Market Fund’s policy of investing at least 80% of its

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assets in securities issued by the U.S. government and its agencies and instrumentalities and the Treasury Money Market Fund’s policy of investing at least 80% of its assets in U.S. Treasury securities also may be changed only upon 60 days’ notice to shareholders.

Market Exposure

Each Fund’s principal strategy is to invest in very high-quality money market instruments. Also known as cash equivalent investments, these instruments are considered short-term (i.e., they usually mature in 397 days or less). Each Fund maintains a dollar-weighted average maturity of 60 days or less and a dollar-weighted average life of 120 days or less. Vanguard Prime Money Market Fund invests more than 25% of its assets in securities issued by companies in the financial services industry.

Each Fund is subject to income risk, which is the chance that the Fund’s income will decline because of falling interest rates. A fund’s income declines when interest rates fall because the fund then must invest new cash flow and cash from maturing instruments in lower-yielding instruments. Because each Fund’s income is based on short-term interest rates—which can fluctuate significantly over short periods—income risk is expected to be high.

A low interest rate environment could adversely affect each Fund’s return. Low interest rates could prevent the Fund from providing a positive yield and/or make it difficult to maintain a stable share price of $1.

Security Selection

Vanguard, advisor to the Funds, selects high-quality money market instruments. Each Fund generally focuses on securities of a particular class of issuer (the U.S. government, U.S. governmental agencies, or nongovernmental issuers).

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Each Fund is subject to manager risk, which is the chance that poor security selection will cause the Fund to underperform relevant benchmarks or other funds with a similar investment objective.

Plain Talk About Credit Quality

A money market instrument’s credit quality is an assessment of the issuer’s ability to pay interest and, ultimately, to repay the principal. The lower the credit quality, the greater the perceived chance that the issuer will default, or fail to meet its payment obligations. Direct U.S. Treasury obligations, along with other securities backed by the “full faith and credit” of the U.S. government, generally are determined to have the highest credit quality. All things being equal, money market instruments with greater credit risk offer higher yields.

The Prime Money Market Fund invests in high-quality commercial paper, U.S. Treasury and agency securities, certificates of deposit, banker’s acceptances, and other money market securities. To be considered high quality, a security must be determined by Vanguard to present minimal credit risk based in part on a consideration of maturity, portfolio diversification, portfolio liquidity, and credit quality. The Prime Money Market Fund also invests in short-term corporate, state, and municipal obligations that are considered high quality, as well as in securities that are considered suitable for the Federal Money Market Fund as described in this prospectus.

The Prime Money Market Fund is subject to industry concentration risk, which is the chance that the Fund‘s performance will be significantly affected, for better or for worse, by developments in the financial services industry.

More than 25% of the Fund’s assets are invested in instruments issued by companies in the financial services industry, such as U.S. and foreign banks, insurance companies, real estate-related companies (i.e., companies having at least 50% of their assets, revenues, or net income related to, or derived from, the real estate industry), securities firms, leasing companies, and other companies principally engaged in providing financial services to consumers and industry. These investments include, among others, bank obligations, high-quality asset-backed securities, and securities issued by the automobile finance industry. Because of this concentration, changes in economic, regulatory, and political conditions that affect financial services companies could have a significant effect on the Fund. These conditions include changes in interest rates and defaults in payments by borrowers.

The Fund may also invest in Eurodollar and Yankee obligations, which include certificates of deposit issued in U.S. dollars by foreign banks and foreign branches of

market instruments, such as income risk and credit risk. Additional risks of Eurodollar and Yankee obligations include the chance that a foreign government will not let U.S. dollar-denominated assets leave the country, the chance that the banks that issue Eurodollar obligations will not be subject to the same regulations as U.S. banks, and the chance that adverse political or economic developments will affect investments in a foreign country. Before the Fund’s advisor selects a Eurodollar or Yankee obligation, however, any foreign issuer undergoes the same credit-quality analysis and tests of financial strength as those for the issuers of domestic securities.

The Federal Money Market Fund invests primarily in securities issued by U.S. governmental agencies and instrumentalities whose interest and principal payments are backed by the full faith and credit of the U.S. government, such as those issued by the U.S. Treasury and the Government National Mortgage Association (GNMA). The Fund also may invest in securities issued by U.S. governmental agencies and instrumentalities whose interest and principal payments are neither guaranteed by the U.S. Treasury nor backed by the full faith and credit of the U.S. government. These agencies and instrumentalities include, among others, the Federal Home Loan Banks, the Federal National Mortgage Association, and the Federal Home Loan Mortgage Corporation.

The Treasury Money Market Fund invests solely in securities whose interest and principal payments are backed by the full faith and credit of the U.S. government. At least 80% of the Fund’s assets will be invested in U.S. Treasury securities. The remainder of the Fund’s assets may include securities issued by U.S. governmental agencies such as the GNMA, the Small Business Administration, and the Federal Financing Bank.

The market values of U.S. government and agency securities and U.S. Treasury securities are subject to fluctuation and the expectation that the U.S. Treasury will be able to honor its obligations.

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Each Fund is subject, to a limited extent, to credit risk, which is the chance that the issuer of a security will fail to pay interest or principal in a timely manner or that negative perceptions of the issuer’s ability to make such payments will cause the price of that security to decline.

The three Funds differ mainly in terms of credit risk. Overall, each Fund’s investments are in securities considered to be of high credit quality.

In relative terms, the Treasury Money Market Fund, which invests in securities backed by the full faith and credit of the U.S. government, offers the lowest credit risk—and generally the lowest yield—of the three Funds.

Because many of the securities included in the Federal Money Market Fund are not backed by the full faith and credit of the U.S. government, the potential credit risk and yield for the Fund are somewhat higher than for the Treasury Money Market Fund.

Although the credit quality of the securities it invests in is very high, the Prime Money Market Fund faces more risk because it invests in money market securities issued by private companies. It is possible that one or more of these companies may experience financial difficulties and, as a result, may fail to pay interest to the Fund or to return the Fund’s principal when repayment is due. Therefore, the Prime Money Market Fund presents the highest credit risk—and generally offers the highest yield—of the three Funds.

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Under certain circumstances, the exposure to a single issuer could cause the Prime Money Market Fund or the Federal Money Market Fund to fail to maintain a share price of $1.

Although each Fund invests in high-quality money market instruments, the three Funds are not insured or guaranteed by the Federal Deposit Insurance Corporation or any other agency of the U.S. government.

The Prime Money Market and Federal Money Market Funds each reserve the right to invest in repurchase agreements, which are subject to specific risks.

Repurchase agreements carry several risks. For instance, if the seller is unable to repurchase the securities as promised, a Fund may experience a loss when trying to sell the securities to another buyer. Also, if the seller becomes insolvent, a bankruptcy court may determine that the securities do not belong to the Fund and order that the securities be used to pay off the seller’s debts. The Funds‘ advisor believes that these risks can be controlled through careful security and counterparty selection and monitoring.

Each Fund reserves the right to invest, to a limited extent, in adjustable-rate securities, which are a type of derivative.

An adjustable-rate security’s interest rate, as the name implies, is not set; instead, it fluctuates periodically. Generally, the security’s yield is based on a U.S. dollar-based interest rate benchmark such as the federal funds rate, the 90-day U.S. Treasury bill rate, or another reference rate. Adjustable-rate securities reset their yields on a periodic basis (e.g., daily, weekly, or quarterly) or upon a change in the benchmark interest rate. These yields are closely correlated to changes in money market interest rates.

The Funds will not use derivatives for speculation or for the purpose of leveraging (magnifying) investment returns.

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Plain Talk About Derivatives

A derivative is a financial contract whose value is based on the value of a financial asset (such as a stock, a bond, or a currency), a money market benchmark (such as U.S. Treasury bill rates or the federal funds effective rate), a physical asset (such as gold, oil, or wheat), a market index, or a reference rate.

In addition, the Prime Money Market and Federal Money Market Funds may each invest up to 5% of its net assets in illiquid securities. These are investments that the Fund reasonably expects cannot be sold or disposed of in current market conditions in seven calendar days or less without the sale or disposition significantly changing the market value of the investment.

Plain Talk About Weighted Average Maturity and Weighted Average Life

A money market fund will maintain a dollar-weighted average maturity (WAM) of 60 days or less and a dollar-weighted average life (WAL) of 120 days or less. For purposes of calculating a fund’s WAM, the maturity of certain longer-term adjustable-rate securities held in the portfolio will generally be the period remaining until the next interest rate adjustment. When calculating its WAL, the maturity for these adjustable-rate securities will generally be the final maturity date—the date on which principal is expected to be returned in full. Maintaining a WAL of 120 days or less limits a fund’s ability to invest in longer-term adjustable-rate securities, which are generally more sensitive to changes in interest rates, particularly in volatile markets.

Cash Management

Each Fund‘s daily cash balance may be invested in Vanguard Market Liquidity Fund and/or Vanguard Municipal Cash Management Fund (the CMT Funds), which are low-cost money market funds. When investing in a Vanguard CMT Fund, each Fund bears its proportionate share of the expenses of the CMT Fund in which it invests. Vanguard receives no additional revenue from Fund assets invested in a Vanguard CMT Fund.

Methods Used to Meet Redemption Requests

Under normal circumstances, each Fund typically expects to meet redemptions with positive cash flows. When this is not an option, each Fund seeks to maintain its risk exposure by selling a cross section of the Fund’s holdings to meet redemptions, while also factoring in transaction costs. Additionally, a Fund may work with larger clients to implement their redemptions in a manner that is least disruptive to the portfolio; see

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“Potentially disruptive redemptions” under Redeeming Shares in the Investing With Vanguard section.

Under certain circumstances, including under stressed market conditions, there are additional tools that each Fund may use in order to meet redemptions, including advancing the settlement of market trades with counterparties to match investor redemption payments or delaying settlement of an investor’s transaction to match trade settlement within regulatory requirements. A Fund may also suspend payment of redemption proceeds for up to seven days; see “Emergency circumstances” under Redeeming Shares in the Investing With Vanguard section. Additionally under these unusual circumstances, a Fund may borrow money (subject to certain regulatory conditions and if available under board-approved procedures) through an interfund lending facility or through a bank line-of-credit, including a joint committed credit facility, in order to meet redemption requests.

Temporary Investment Measures

Each Fund may temporarily depart from its normal investment policies and strategies—for instance, by allocating substantial assets to cash equivalent investments—in response to adverse or unusual market, economic, political, or other conditions. In doing so, each Fund may succeed in avoiding losses but may otherwise fail to achieve its investment objective.

Frequent Trading or Market-Timing

Vanguard anticipates that shareholders will purchase and sell shares of money market funds frequently because these funds are designed to offer investors a liquid investment. For this reason, the board of trustees of each Fund has determined that it is not necessary to adopt policies and procedures designed to detect and deter frequent trading and market-timing in the money market fund shares. For information on frequent-trading limits of other Vanguard funds, please see the appropriate fund’s prospectus.

The Funds and Vanguard

Each Fund is a member of The Vanguard Group, a family of over 200 funds holding assets of approximately $4.9 trillion. All of the funds that are members of The Vanguard Group (other than funds of funds) share in the expenses associated with administrative services and business operations, such as personnel, office space, and equipment.

Vanguard Marketing Corporation provides marketing services to the funds. Although fund shareholders do not pay sales commissions or 12b-1 distribution fees, each fund (other than a fund of funds) or each share class of a fund (in the case of a fund with multiple share classes) pays its allocated share of the Vanguard funds’ marketing costs.

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Plain Talk About Vanguard’s Unique Corporate Structure

The Vanguard Group is owned jointly by the funds it oversees and thus indirectly by the shareholders in those funds. Most other mutual funds are operated by management companies that are owned by third parties—either public or private stockholders—not by the funds they serve.

Investment Advisor

The Vanguard Group, Inc., P.O. Box 2600, Valley Forge, PA 19482, which began operations in 1975, serves as advisor to the Funds through its Fixed Income Group. As of August 31, 2018, Vanguard served as advisor for approximately $4.2 trillion in assets. Vanguard provides investment advisory services to the Funds pursuant to the Funds’ Service Agreement and subject to the supervision and oversight of the trustees and officers of the Funds.

For the fiscal year ended August 31, 2018, the advisory expenses represented an effective annual rate of less than 0.01% of each Fund‘s average net assets.

Under the terms of an SEC exemption, the Funds‘ board of trustees may, without prior approval from shareholders, change the terms of an advisory agreement with a third-party investment advisor or hire a new third-party investment advisor—either as a replacement for an existing advisor or as an additional advisor. Any significant change in a Fund’s advisory arrangements will be communicated to shareholders in writing. As the Funds‘ sponsor and overall manager, Vanguard may provide investment advisory services to a Fund at any time. Vanguard may also recommend to the board of trustees that an advisor be hired, terminated, or replaced or that the terms of an existing advisory agreement be revised. The Funds have filed an application seeking a similar SEC exemption with respect to investment advisors that are wholly owned subsidiaries of Vanguard. If the exemption is granted, the Funds may rely on the new SEC relief.

For a discussion of why the board of trustees approved each Fund’s investment advisory arrangement, see the most recent annual report to shareholders covering the fiscal year ended August 31.

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The managers primarily responsible for the day-to-day management of the Funds are:

John C. Lanius, Portfolio Manager at Vanguard. He has been with Vanguard since 1996, has worked in investment management since 1997, has managed investment portfolios since 2004, and has managed the Federal Money Market Fund since 2007. Education: B.A., Middlebury College.

Nafis T. Smith, Portfolio Manager at Vanguard. He has been with Vanguard since 2003, has worked in investment management since 2005, has managed investment portfolios for Vanguard since 2010, and has managed the Prime Money Market Fund and Treasury Money Market Fund since 2017. Education: B.A., Cornell University.

The Statement of Additional Information provides information about each portfolio manager’s compensation, other accounts under management, and ownership of shares of the Funds.

Dividends, Capital Gains, and Taxes

Fund Distributions

Each Fund distributes to shareholders virtually all of its net income (interest less expenses). Each Fund may also realize capital gains from the sale of its holdings and distribute these gains (net of losses) to shareholders as capital gains distributions. As a money market fund, each Fund’s distributions are expected to consist primarily of income dividends. Income dividends generally are declared daily and distributed monthly. In addition, each Fund may occasionally make a supplemental distribution at some other time during the year.

You can receive distributions of income or capital gains in cash, or you can have them automatically reinvested in more shares of the Fund. However, if you are investing through an employer-sponsored retirement or savings plan, your distributions will be automatically reinvested in additional Fund shares.

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Basic Tax Points

Investors in taxable accounts should be aware of the following basic federal income tax points:

• Distributions are taxable to you whether or not you reinvest these amounts in additional Fund shares.

• Distributions declared in December—if paid to you by the end of January—are taxable as if received in December.

• Any income dividend distribution or short-term capital gains distribution that you receive is taxable to you as ordinary income.

• Any distribution of net long-term capital gains is taxable to you as long-term capital gains, no matter how long you have owned shares in the Fund. Because of the short-term nature of each Fund’s holdings, the Fund generally does not expect to make distributions of net long-term capital gains.

• If you redeem or exchange shares when the Prime Money Market Fund has imposed a liquidity fee, then the amount you receive for your redemption will be reduced by the amount of the liquidity fee and will generally cause you to recognize a loss for tax purposes equal to the amount of that fee. If the Prime Money Market Fund has imposed a liquidity fee, it is possible that the Fund may need to distribute to its remaining shareholders all or a portion of the amount of the fee collected. The distribution may be taxable to you as ordinary income or may constitute a non-taxable return of capital.

• Any conversion between classes of shares of the same fund is a nontaxable event. By contrast, an exchange between classes of shares of different funds is a taxable event.

• Vanguard (or your intermediary) will send you a statement each year showing the tax status of all of your distributions.

Individuals, trusts, and estates whose income exceeds certain threshold amounts are subject to a 3.8% Medicare contribution tax on “net investment income.” Net investment income takes into account distributions paid by the Fund and capital gains from any sale or exchange of Fund shares.

Income dividends and capital gains distributions that you receive may be subject to state and local income taxes. Depending on your state’s rules, however, any dividends attributable to interest earned on direct obligations of the U.S. government may be exempt from state and local taxes. Vanguard will notify you each year how much, if any, of your dividends may qualify for this exemption.

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This prospectus provides general tax information only. If you are investing through a tax-advantaged account, such as an IRA or an employer-sponsored retirement or savings plan, special tax rules apply. Please consult your tax advisor for detailed information about any tax consequences for you.

General Information

Backup withholding. By law, Vanguard must withhold 24% of any taxable distributions or redemptions from your account if you do not:

• Provide your correct taxpayer identification number.
• Certify that the taxpayer identification number is correct.
• Confirm that you are not subject to backup withholding.

Similarly, Vanguard (or your intermediary) must withhold taxes from your account if the IRS instructs us to do so.

Foreign investors. Vanguard funds offered for sale in the United States (Vanguard U.S. funds), including the Funds offered in this prospectus, are not widely available outside the United States. Non-U.S. investors should be aware that U.S. withholding and estate taxes and certain U.S. tax reporting requirements may apply to any investments in Vanguard U.S. funds. Foreign investors should visit the Non-U.S. investors page on our website at vanguard.com for information on Vanguard’s non-U.S. products.

Invalid addresses. If an income dividend distribution or capital gains distribution check mailed to your address of record is returned as undeliverable, Vanguard will automatically reinvest the distribution and all future distributions until you provide us with a valid mailing address. Reinvestments will receive the net asset value calculated on the date of the reinvestment.

Share Price

Share price, also known as net asset value (NAV), is calculated each business day as of the close of regular trading on the New York Stock Exchange (NYSE), generally 4 p.m., Eastern time. In the rare event the NYSE experiences unanticipated disruptions and is unavailable at the close of the trading day, NAVs will be calculated as of the close of regular trading on the Nasdaq (or another alternate exchange if the Nasdaq is unavailable, as determined at Vanguard’s discretion), generally 4 p.m., Eastern time. The NAV per share for the Federal Money Market and Treasury Money Market Funds is computed by dividing the total assets, minus liabilities, of the Fund by the number of Fund shares outstanding. Each share class of the Prime Money Market Fund has its own NAV, which is computed by dividing the total assets, minus liabilities, allocated to the share class by the number of Fund shares outstanding for that class. On U.S. holidays or other days when the NYSE is closed, the NAV is not calculated, and the Funds do not sell or redeem

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shares. However, on those days the value of a Fund’s assets may be affected to the extent that the Fund holds securities that change in value on those days (such as foreign securities that trade on foreign markets that are open).

The instruments held by a Vanguard retail or government money market fund are valued on the basis of amortized cost. The values of any mutual fund shares, including institutional money market fund shares, held by a fund are based on the NAVs of the shares. The values of any ETF shares or closed-end fund shares held by a fund are based on the market value of the shares.

Although the stable share price is not guaranteed, the NAV of Vanguard retail and government money market funds is expected to remain at $1 per share. Instruments are purchased and managed with that goal in mind.

Vanguard money market fund yields are available on our website at vanguard.com/prices.

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Financial Highlights

The following financial highlights tables are intended to help you understand each Fund’s financial performance for the periods shown, and certain information reflects financial results for a single Fund share. The total returns in each table represent the rate that an investor would have earned or lost each period on an investment in the Fund (assuming reinvestment of all distributions). This information has been obtained from the financial statements audited by PricewaterhouseCoopers LLP, an independent registered public accounting firm, whose report—along with each Fund’s financial statements—is included in the Funds‘ most recent annual report to shareholders. You may obtain a free copy of the latest annual or semiannual report by visiting vanguard.com or by contacting Vanguard by telephone or mail.

1 Calculated based on average shares outstanding. 2 Distribution was less than $0.0001 per share.

3 Total returns do not include account service fees that may have applied in the periods shown.

4 Vanguard and the board of trustees have agreed to temporarily limit certain net operating expenses in excess of the Fund’s daily yield in order to maintain a zero or positive yield for the Fund. Vanguard and the board of trustees may terminate the temporary expense limitation at any time. The Fund is not obligated to repay this amount to Vanguard. The ratio of total expenses to average net assets before an expense reduction was 0.16% for 2016, 0.16% for 2015, and 0.16% for 2014. For the years ended August 31, 2018 and 2017, there were no expense reductions. For additional information, see Note B in the Notes to Financial Statements section of the Fund’s current annual report to shareholders dated August 31, 2018.

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1 Calculated based on average shares outstanding. 2 Distribution was less than $0.0001 per share.

3 Total returns do not include account service fees that may have applied in the periods shown.

4 Vanguard and the board of trustees have agreed to temporarily limit certain net operating expenses in excess of the Fund’s daily yield in order to maintain a zero or positive yield for the Fund. Vanguard and the board of trustees may terminate the temporary expense limitation at any time. The Fund is not obligated to repay this amount to Vanguard. The ratio of total expenses to average net assets before an expense reduction was 0.11% for 2016, 0.11% for 2015, and 0.11% for 2014. For the years ended August 31, 2018 and 2017, there were no expense reductions. For additional information, see Note B in the Notes to Financial Statements section of the Fund’s current annual report to shareholders dated August 31, 2018.

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1 Calculated based on average shares outstanding. 2 Distribution was less than $0.0001 per share.

3 Total returns do not include account service fees that may have applied in the periods shown.

4 Vanguard and the board of trustees have agreed to temporarily limit certain net operating expenses in excess of the Fund’s daily yield in order to maintain a zero or positive yield for the Fund. Vanguard and the board of trustees may terminate the temporary expense limitation at any time. The Fund is not obligated to repay this amount to Vanguard. The ratio of total expenses to average net assets before an expense reduction was 0.09% for 2016, 0.09% for 2015, and 0.09% for 2014. For the years ended August 31, 2018 and 2017, there were no expense reductions. For additional information, see Note B in the Notes to Financial Statements section of the Fund’s current annual report to shareholders dated August 31, 2018.

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Investing With Vanguard

This section of the prospectus explains the basics of doing business with Vanguard. Vanguard fund shares can be held directly with Vanguard or indirectly through an intermediary, such as a bank, a broker, or an investment advisor. If you hold Vanguard fund shares directly with Vanguard, you should carefully read each topic within this section that pertains to your relationship with Vanguard. If you hold Vanguard fund shares indirectly through an intermediary (including shares held in a brokerage account through Vanguard Brokerage Services^®), please see Investing With Vanguard Through Other Firms, and also refer to your account agreement with the intermediary for information about transacting in that account. If you hold Vanguard fund shares through an employer-sponsored retirement or savings plan, please see Employer-Sponsored Plans. Vanguard reserves the right to change the following policies without notice. Please call or check online for current information. See Contacting Vanguard.

For Vanguard fund shares held directly with Vanguard, each fund you hold in an account is a separate “fund account.” For example, if you hold three funds in a nonretirement account titled in your own name, two funds in a nonretirement account titled jointly with your spouse, and one fund in an individual retirement account, you have six fund accounts—and this is true even if you hold the same fund in multiple accounts. Note that each reference to “you” in this prospectus applies to any one or more registered account owners or persons authorized to transact on your account.

Purchasing Shares

Vanguard reserves the right, without notice, to increase or decrease the minimum amount required to open, convert shares to, or maintain a fund account or to add to an existing fund account.

Investment minimums may differ for certain categories of investors.

Account Minimums for Investor Shares

To open and maintain an account. For the Prime Money Market and Federal Money Market Funds—$3,000. For the Treasury Money Market Fund—$50,000. For the Federal Money Market Fund and the Treasury Money Market Fund, financial intermediaries, institutional, and Vanguard-advised clients should contact Vanguard for information on special eligibility rules that may apply to them regarding Investor Shares. If you are investing through an intermediary, please contact that firm directly for more information regarding your eligibility.

To add to an existing account. Generally $1.

How to Initiate a Purchase Request

Be sure to check Exchanging Shares and Other Rules You Should Know before placing your purchase request.

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Online. You may open certain types of accounts, request a purchase of shares, and request an exchange through our website or our mobile application if you are registered for online access.

By telephone. You may call Vanguard to begin the account registration process or request that the account-opening forms be sent to you. You may also call Vanguard to request a purchase of shares in your account or to request an exchange. See

Contacting Vanguard.

By mail. You may send Vanguard your account registration form and check to open a new fund account. To add to an existing fund account, you may send your check with an Invest-by-Mail form (from a transaction confirmation or your account statement) or with a deposit slip (available online). For a list of Vanguard addresses, see Contacting Vanguard.

How to Pay for a Purchase

By electronic bank transfer. You may purchase shares of a Vanguard fund through an electronic transfer of money from a bank account. To establish the electronic bank transfer service on an account, you must designate the bank account online, complete a form, or fill out the appropriate section of your account registration form. After the service is set up on your account, you can purchase shares by electronic bank transfer on a regular schedule (Automatic Investment Plan) or upon request. Your purchase request can be initiated online (if you are registered for online access), by telephone, or by mail.

By wire. Wiring instructions vary for different types of purchases. Please call Vanguard for instructions and policies on purchasing shares by wire. See Contacting Vanguard.

By check. You may make initial or additional purchases to your fund account by sending a check with a deposit slip or by utilizing our mobile application if you are registered for online access. Also see How to Initiate a Purchase Request. Make your check payable to Vanguard and include the appropriate fund number (e.g., Vanguard—xx). For a list of Fund numbers (for Funds in this prospectus), see Additional Information.

By exchange. You may purchase shares of a Vanguard fund using the proceeds from the simultaneous redemption of shares of another Vanguard fund. You may initiate an exchange online (if you are registered for online access), by telephone, or by mail with an exchange form. See Exchanging Shares.

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Trade Date

The trade date for any purchase request received in good order will depend on the day and time Vanguard receives your request, the manner in which you are paying, and the type of fund you are purchasing. Your purchase will be executed using the NAV as calculated on the trade date. NAVs are calculated only on days that the NYSE is open for trading (a business day).

For purchases by check into all funds other than money market funds and for purchases by exchange, wire, or electronic bank transfer (not using an Automatic Investment Plan) into all funds: If the purchase request is received by Vanguard on a business day before the close of regular trading on the NYSE (generally 4 p.m., Eastern time), the trade date for the purchase will be the same day. If the purchase request is received on a business day after the close of regular trading on the NYSE, or on a nonbusiness day, the trade date for the purchase will be the next business day.

For purchases by check into money market funds: If the purchase request is received by Vanguard on a business day before the close of regular trading on the NYSE (generally 4 p.m., Eastern time), the trade date for the purchase will be the next business day. If the purchase request is received on a business day after the close of regular trading on the NYSE, or on a nonbusiness day, the trade date for the purchase will be the second business day following the day Vanguard receives the purchase request. Because money market instruments must be purchased with federal funds and it takes a money market mutual fund one business day to convert check proceeds into federal funds, the trade date for the purchase will be one business day later than for other funds.

For purchases by electronic bank transfer using an Automatic Investment Plan: Your trade date generally will be the date you selected for withdrawal of funds from your designated bank account. Your bank account generally will be debited on the business day after your trade date. If the date you selected for withdrawal of funds from your bank account falls on a weekend, holiday, or other nonbusiness day, your trade date generally will be the previous business day. For retirement accounts, if the date you selected for withdrawal of funds from your designated bank account falls on the last business day of the year, your trade date will be the first business day of the following year. Please note that if you select the first of the month for automated withdrawals from your designated bank account, trades designated for January 1 will receive the next business day’s trade date.

If your purchase request is not accurate and complete, it may be rejected. See Other Rules You Should Know—Good Order.

For further information about purchase transactions, consult our website at vanguard.com or see Contacting Vanguard.

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Earning Dividends

You generally begin earning dividends on the business day following your trade date. When buying money market fund shares through a federal funds wire on a business day, however, you generally can begin earning dividends immediately by making a purchase request by telephone to Vanguard before 10:45 a.m., Eastern time (2 p.m., Eastern time, for Vanguard Prime Money Market Fund; 12:30 p.m., Eastern time, for Vanguard Federal Money Market Fund).

Other Purchase Rules You Should Know

Check purchases. All purchase checks must be written in U.S. dollars and must be drawn on a U.S. bank and be accompanied by good order instructions. Vanguard does not accept cash, traveler’s checks, starter checks, or money orders. In addition, Vanguard may refuse checks that are not made payable to Vanguard.

New accounts. We are required by law to obtain from you certain personal information that we will use to verify your identity. If you do not provide the information, we may not be able to open your account. If we are unable to verify your identity, Vanguard reserves the right, without notice, to close your account or take such other steps as we deem reasonable. Certain types of accounts may require additional documentation.

Refused or rejected purchase requests. Vanguard reserves the right to stop selling fund shares or to reject any purchase request at any time and without notice, including, but not limited to, purchases requested by exchange from another Vanguard fund. This also includes the right to reject any purchase request because the investor has a history of frequent trading or because the purchase may negatively affect a fund’s operation or performance.

Large purchases. Call Vanguard before attempting to invest a large dollar amount.

No cancellations. Vanguard will not accept your request to cancel any purchase request once processing has begun. Please be careful when placing a purchase request.

Converting Shares

When a conversion occurs, you receive shares of one class in place of shares of another class of the same fund. At the time of conversion, the dollar value of the “new” shares you receive equals the dollar value of the “old” shares that were converted. In other words, the conversion has no effect on the value of your investment in the fund at the time of the conversion. However, the number of shares you own after the conversion may be greater than or less than the number of shares you owned before the conversion, depending on the NAVs of the two share classes.

Vanguard will not accept your request to cancel any self-directed conversion request once processing has begun. Please be careful when placing a conversion request.

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A conversion between share classes of the same fund is a nontaxable event.

Trade Date

The trade date for any conversion request received in good order will depend on the day and time Vanguard receives your request. Your conversion will be executed using the NAVs of the different share classes on the trade date. NAVs are calculated only on days that the NYSE is open for trading (a business day).

For a conversion request received by Vanguard on a business day before the close of regular trading on the NYSE (generally 4 p.m., Eastern time), the trade date will be the same day. For a conversion request received on a business day after the close of regular trading on the NYSE, or on a nonbusiness day, the trade date will be the next business day. See Other Rules You Should Know.

Conversions From Investor Shares to Admiral Shares

Self-directed conversions. If your account balance in the Prime Money Market Fund is at least $5 million, you may ask Vanguard to convert your Investor Shares to Admiral Shares. You may request a conversion through our website (if you are registered for online access), by telephone, or by mail. Financial intermediaries and Vanguard-advised clients should contact Vanguard for information on special eligibility rules that may apply to them regarding Admiral Shares. See Contacting Vanguard. If you are investing through an intermediary, please contact that firm directly for more information regarding your eligibility.

Automatic conversions. Vanguard conducts periodic reviews of account balances and may, if your account balance in the Fund exceeds $5 million, automatically convert your Investor Shares to Admiral Shares. You will be notified before an automatic conversion occurs and will have an opportunity to instruct Vanguard not to effect the conversion. Financial intermediaries and Vanguard-advised clients should contact Vanguard for information on special eligibility rules that may apply to them regarding Admiral Shares. If you are investing through an intermediary, please contact that firm directly for more information regarding your eligibility.

Mandatory Conversions to Investor Shares

If an account no longer meets the balance requirements for Admiral Shares, Vanguard may automatically convert the shares in the account to Investor Shares. A decline in the account balance because of market movement may result in such a conversion. Vanguard will notify the investor in writing before any mandatory conversion occurs.

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Redeeming Shares

How to Initiate a Redemption Request

Be sure to check Exchanging Shares and Other Rules You Should Know before placing your redemption request.

Online. You may request a redemption of shares or request an exchange through our website or our mobile application if you are registered for online access.

By telephone. You may call Vanguard to request a redemption of shares or an exchange. See Contacting Vanguard.

By mail. You may send a form (available online) to Vanguard to redeem from a fund account or to make an exchange. See Contacting Vanguard.

By writing a check. If you have established the checkwriting service on your account, you can redeem shares by writing a check for $250 or more.

How to Receive Redemption Proceeds

By electronic bank transfer. You may have the proceeds of a fund redemption sent directly to a designated bank account. To establish the electronic bank transfer service on an account, you must designate a bank account online, complete a special form, or fill out the appropriate section of your account registration form. After the service is set up on your account, you can redeem shares by electronic bank transfer on a regular schedule (Automatic Withdrawal Plan) or upon request. Your redemption request can be initiated online (if you are registered for online access), by telephone, or by mail.

By wire. To receive your proceeds by wire, you may instruct Vanguard to wire your redemption proceeds ($100 minimum) to a previously designated bank account. To establish the wire redemption service, you generally must designate a bank account online, complete a special form, or fill out the appropriate section of your account registration form.

Please note that Vanguard charges a $10 wire fee for outgoing wire redemptions. The fee is assessed in addition to, rather than being withheld from, redemption proceeds and is paid directly to the fund. For example, if you redeem $100 via a wire, you will receive the full $100, and your fund account will also be assessed the $10 fee by redeeming additional fund shares. If you redeem your entire fund account, your redemption proceeds will be reduced by the fee amount. The wire fee does not apply to accounts held by Flagship and Flagship Select clients; accounts held through intermediaries, including Vanguard Brokerage Services; or accounts held by institutional clients.

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By exchange. You may have the proceeds of a Vanguard fund redemption invested directly in shares of another Vanguard fund. You may initiate an exchange online (if you are registered for online access), by telephone, or by mail. See Exchanging Shares.

By check. If you have not chosen another redemption method, Vanguard will mail you a redemption check, generally payable to all registered account owners, normally within two business days of your trade date, and generally to the address of record.

Trade Date

The trade date for any redemption request received in good order will depend on the day and time Vanguard receives your request and the manner in which you are redeeming. Your redemption will be executed using the NAV as calculated on the trade date. NAVs are calculated only on days that the NYSE is open for trading (a business day).

For redemptions by check, exchange, or wire: If the redemption request is received by Vanguard on a business day before the close of regular trading on the NYSE (generally 4 p.m., Eastern time), the trade date will be the same day. If the redemption request is received on a business day after the close of regular trading on the NYSE, or on a nonbusiness day, the trade date will be the next business day.

• Note on timing of wire redemptions from money market funds: For telephone requests received by Vanguard on a business day before 10:45 a.m., Eastern time (2 p.m., Eastern time, for Vanguard Prime Money Market Fund; 12:30 p.m., Eastern time, for Vanguard Federal Money Market Fund), the redemption proceeds generally will leave Vanguard by the close of business the same day. For telephone requests received by Vanguard on a business day after those cut-off times, or on a nonbusiness day, and for all requests other than by telephone, the redemption proceeds generally will leave Vanguard by the close of business on the next business day.

• Note on timing of wire redemptions from all other funds: For requests received by Vanguard on a business day before the close of regular trading on the NYSE (generally 4 p.m., Eastern time), the redemption proceeds generally will leave Vanguard by the close of business on the next business day. For requests received by Vanguard on a business day after the close of regular trading on the NYSE, or on a nonbusiness day, the redemption proceeds generally will leave Vanguard by the close of business on the second business day after Vanguard receives the request.

For redemptions by electronic bank transfer using an Automatic Withdrawal Plan: Your trade date generally will be the date you selected for withdrawal of funds (redemption of shares) from your Vanguard account. Proceeds of redeemed shares generally will be credited to your designated bank account two business days after your trade date. If the date you selected for withdrawal of funds from your Vanguard

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account falls on a weekend, holiday, or other nonbusiness day, your trade date generally will be the previous business day. For retirement accounts, if the date you selected for withdrawal of funds from your Vanguard account falls on the last day of the year and if that date is a holiday, your trade date will be the first business day of the following year. Please note that if you designate the first of the month for automated withdrawals, trades designated for January 1 will receive the next business day’s trade date.

For redemptions by electronic bank transfer not using an Automatic Withdrawal Plan: If the redemption request is received by Vanguard on a business day before the close of regular trading on the NYSE (generally 4 p.m., Eastern time), the trade date will be the same day. If the redemption request is received on a business day after the close of regular trading on the NYSE, or on a nonbusiness day, the trade date will be the next business day.

If your redemption request is not accurate and complete, it may be rejected. If we are unable to send your redemption proceeds by wire or electronic bank transfer because the receiving institution rejects the transfer, Vanguard will make additional efforts to complete your transaction. If Vanguard is still unable to complete the transaction, we may send the proceeds of the redemption to you by check, generally payable to all registered account owners, or use your proceeds to purchase new shares of the fund from which you sold shares for the purpose of the wire or electronic bank transfer transaction. See Other Rules You Should Know—Good Order.

If your redemption request is received in good order, we typically expect that redemption proceeds will be paid by a Fund within one business day of the trade date; however, in certain circumstances, investors may experience a longer settlement period at the time of the transaction. For further information, see “Potentially disruptive redemptions” and “Emergency circumstances.”

For further information about redemption transactions, consult our website at vanguard.com or see Contacting Vanguard.

Earning Dividends

You generally will continue earning dividends until the first business day following your trade date. Generally, there are two exceptions to this rule: (1) If you redeem shares by writing a check against your account, the shares will stop earning dividends on the day that your check posts to your account; and (2) For money market funds, if you redeem shares with a same-day wire request before 10:45 a.m., Eastern time, on a business day (2 p.m., Eastern time, for Vanguard Prime Money Market Fund; 12:30 p.m., Eastern time, for Vanguard Federal Money Market Fund), the shares will stop earning dividends that same day.

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Other Redemption Rules You Should Know

Documentation for certain accounts. Special documentation may be required to redeem from certain types of accounts, such as trust, corporate, nonprofit, or retirement accounts. Please call us before attempting to redeem from these types of accounts.

Potentially disruptive redemptions. Vanguard reserves the right to pay all or part of a redemption in kind—that is, in the form of securities—if we reasonably believe that a cash redemption would negatively affect the fund’s operation or performance or that the shareholder may be engaged in market-timing or frequent trading. Under these circumstances, Vanguard also reserves the right to delay payment of the redemption proceeds for up to seven calendar days. By calling us before you attempt to redeem a large dollar amount, you may avoid in-kind or delayed payment of your redemption.

Recently purchased shares. Although you can redeem shares at any time, proceeds may not be made available to you until the fund collects payment for your purchase. This may take up to seven calendar days for shares purchased by check or by electronic bank transfer. If you have written a check on a fund with checkwriting privileges, that check may be rejected if your fund account does not have a sufficient available balance.

Share certificates. Share certificates are no longer issued for Vanguard funds. Shares currently held in certificates cannot be redeemed, exchanged, converted, or transferred (reregistered) until you return the certificates (unsigned) to Vanguard by registered mail. For the correct address, see Contacting Vanguard.

Address change. If you change your address online or by telephone, there may be up to a 15-day restriction on your ability to request check redemptions online and by telephone. You can request a redemption in writing (using a form available online) at any time. Confirmations of address changes are sent to both the old and new addresses.

Payment to a different person or address. At your request, we can make your redemption check payable, or wire your redemption proceeds, to a different person or send it to a different address. However, this generally requires the written consent of all registered account owners and may require additional documentation, such as a signature guarantee or a notarized signature. You may obtain a signature guarantee from some commercial or savings banks, credit unions, trust companies, or member firms of a U.S. stock exchange.

No cancellations. Vanguard will not accept your request to cancel any redemption request once processing has begun. Please be careful when placing a redemption request.

Emergency circumstances. Vanguard funds can postpone payment of redemption proceeds for up to seven calendar days. In addition, Vanguard funds can suspend redemptions and/or postpone payments of redemption proceeds beyond seven

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calendar days at times when the NYSE is closed or during emergency circumstances, as determined by the SEC. In connection with a determination by the board of trustees, in accordance with Rule 22e-3 under the Investment Company Act of 1940, a money market fund may suspend redemptions and postpone payment of redemption proceeds in order to facilitate an orderly liquidation of the fund. In addition, in accordance with Rule 2a-7 under the Investment Company Act of 1940, the board of trustees of a retail or institutional money market fund may implement liquidity fees and redemption gates if a retail or institutional money market fund‘s weekly liquid assets fall below established thresholds.

Exchanging Shares

An exchange occurs when you use the proceeds from the redemption of shares of one Vanguard fund to simultaneously purchase shares of a different Vanguard fund. You can make exchange requests online (if you are registered for online access), by telephone, or by mail. See Purchasing Shares and Redeeming Shares.

If the NYSE is open for regular trading (generally until 4 p.m., Eastern time, on a business day) at the time an exchange request is received in good order, the trade date generally will be the same day. See Other Rules You Should Know—Good Order for additional information on all transaction requests.

Vanguard will not accept your request to cancel any exchange request once processing has begun. Please be careful when placing an exchange request.

Call Vanguard before attempting to exchange a large dollar amount. By calling us before you attempt to exchange a large dollar amount, you may avoid delayed or rejected transactions.

Please note that Vanguard reserves the right, without notice, to revise or terminate the exchange privilege, limit the amount of any exchange, or reject an exchange, at any time, for any reason.

Other Rules You Should Know

Prospectus and Shareholder Report Mailings

When two or more shareholders have the same last name and address, just one summary prospectus (or prospectus) and/or shareholder report may be sent in an attempt to eliminate the unnecessary expense of duplicate mailings. You may request individual prospectuses and reports by contacting our Client Services Department in writing, by telephone, or online. See Contacting Vanguard.

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Vanguard.com

Registration. If you are a registered user of vanguard.com, you can review your account holdings; buy, sell, or exchange shares of most Vanguard funds; and perform most other transactions through our website. You must register for this service online.

Electronic delivery. Vanguard can deliver your account statements, transaction confirmations, prospectuses, certain tax forms, and shareholder reports electronically. If you are a registered user of vanguard.com, you can consent to the electronic delivery of these documents by logging on and changing your mailing preferences under “Account Maintenance.” You can revoke your electronic consent at any time through our website, and we will begin to send paper copies of these documents within 30 days of receiving your revocation.

Telephone Transactions

Automatic. When we set up your account, we will automatically enable you to do business with us by telephone, unless you instruct us otherwise in writing.

Tele-Account^®. To obtain fund and account information through Vanguard’s automated telephone service, you must first establish a Personal Identification Number (PIN) by calling Tele-Account at 800-662-6273.

Proof of a caller’s authority. We reserve the right to refuse a telephone request if the caller is unable to provide the requested information or if we reasonably believe that the caller is not an individual authorized to act on the account. Before we allow a caller to act on an account, we may request the following information:

• Authorization to act on the account (as the account owner or by legal documentation or other means).

• Account registration and address.
• Fund name and account number, if applicable.
• Other information relating to the caller, the account owner, or the account.

Good Order

We reserve the right to reject any transaction instructions that are not in “good order.” Good order generally means that your instructions:

• Are provided by the person(s) authorized in accordance with Vanguard’s policies and procedures to access the account and request transactions.

• Include the fund name and account number.
• Include the amount of the transaction (stated in dollars, shares, or percentage).

Written instructions also must generally be provided on a Vanguard form and include:

• Signature(s)and date from the authorized person(s).

• Signature guarantees or notarized signatures, if required for the type of transaction.

(Call Vanguard for specific requirements.)

• Any supporting documentation that may be required. For Vanguard Prime Money Market Fund, documentation may be required to confirm that the beneficial owner is a natural person.

The requirements vary among types of accounts and transactions. For more information, consult our website at vanguard.com or see Contacting Vanguard.

Vanguard reserves the right, without notice, to revise the requirements for good order.

Future Trade-Date Requests

Vanguard does not accept requests to hold a purchase, conversion, redemption, or exchange transaction for a future date. All such requests will receive trade dates as previously described in Purchasing Shares, Converting Shares, Redeeming Shares, and

Exchanging Shares. Vanguard reserves the right to return future-dated purchase checks.

Accounts With More Than One Owner

If an account has more than one owner or authorized person, Vanguard generally will accept instructions from any one owner or authorized person.

Responsibility for Fraud

Vanguard will not be responsible for any account losses because of fraud if we reasonably believe that the person transacting business on an account is authorized to do so. Please take precautions to protect yourself from fraud. Keep your account information private, and immediately review any account statements or other information that we provide to you. It is important that you contact Vanguard immediately about any transactions or changes to your account that you believe to be unauthorized.

Uncashed Checks

Please cash your distribution or redemption checks promptly. Vanguard will not pay interest on uncashed checks. Vanguard may be required to transfer assets related to uncashed checks to a state under the state’s abandoned property law.

Dormant Accounts

If your account has no activity in it for a period of time, Vanguard may be required to transfer it to a state under the state’s abandoned property law, subject to potential federal or state withholding taxes.

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Unusual Circumstances

If you experience difficulty contacting Vanguard online or by telephone, you can send us your transaction request on a Vanguard form by regular or express mail. See Contacting Vanguard for addresses.

Investing With Vanguard Through Other Firms

You may purchase or sell shares of most Vanguard funds through a financial intermediary, such as a bank, a broker, or an investment advisor. Please consult your financial intermediary to determine which, if any, shares are available through that firm and to learn about other rules that may apply. Your financial intermediary can provide you with account information and any required tax forms. Your financial intermediary will be responsible for taking reasonable actions to assist the retail or institutional money market fund to impose, lift, or modify liquidity fees or redemption gates.

Account Service Fee

Vanguard charges a $20 account service fee on fund accounts that have a balance below $10,000 for any reason, including market fluctuation. The account service fee applies to both retirement and nonretirement fund accounts and will be assessed on fund accounts in all Vanguard funds, regardless of the account minimum. The fee, which will be collected by redeeming fund shares in the amount of $20, will be deducted from a fund account only once per calendar year.

If you register on vanguard.com and elect to receive electronic delivery of statements, reports, and other materials for all of your fund accounts, the account service fee for balances below $10,000 will not be charged, so long as that election remains in effect.

The account service fee also does not apply to the following:

• Money market sweep accounts owned in connection with a Vanguard Brokerage Services account.*

• Accounts held through intermediaries.*
• Accounts held by institutional clients.
• Accounts held by Voyager, Voyager Select, Flagship, and Flagship Select clients.

Eligibility is based on total household assets held at Vanguard, with a minimum of $50,000 to qualify for Vanguard Voyager Services^®, $500,000 for Vanguard Voyager Select Services^®, $1 million for Vanguard Flagship Services^®, and $5 million for Vanguard Flagship Select Services^™. Vanguard determines eligibility by aggregating assets of all qualifying accounts held by the investor and immediate family members who reside at the same address. Aggregate assets include investments in Vanguard mutual funds, Vanguard ETFs^®, certain annuities through Vanguard, the Vanguard 529 Plan, and certain small-business accounts. Assets in employer-sponsored retirement plans for which Vanguard provides recordkeeping services may be included in

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determining eligibility if the investor also has a personal account holding Vanguard mutual funds. Note that assets held in a Vanguard Brokerage Services account (other than Vanguard funds, including Vanguard ETFs) are not included when determining a household’s eligibility.

• Participant accounts in employer-sponsored defined contribution plans.** Please consult your enrollment materials for the rules that apply to your account.

• Section 529 college savings plans.
• Please note that intermediaries, including Vanguard Brokerage Services, may charge
• separate fee.
• The following Vanguard fund accounts have alternative fee structures: SIMPLE

IRAs, certain Individual 403(b)(7) Custodial Accounts, Vanguard Retirement Investment Program pooled plans, and Vanguard Individual 401(k) Plans.

Low-Balance Accounts

Each Fund reserves the right to liquidate a fund account whose balance falls below the account minimum for any reason, including market fluctuation. This liquidation policy applies to nonretirement fund accounts and accounts that are held through intermediaries. Any such liquidation will be preceded by written notice to the investor.

Right to Change Policies

In addition to the rights expressly stated elsewhere in this prospectus, Vanguard reserves the right, without notice, to (1) alter, add, or discontinue any conditions of purchase (including eligibility requirements), redemption, exchange, conversion, service, or privilege at any time; (2) accept initial purchases by telephone; (3) freeze any account and/or suspend account services if Vanguard has received reasonable notice of a dispute regarding the assets in an account, including notice of a dispute between the registered or beneficial account owners, or if Vanguard reasonably believes a fraudulent transaction may occur or has occurred; (4) temporarily freeze any account and/or suspend account services upon initial notification to Vanguard of the death of the shareholder until Vanguard receives required documentation in good order; (5) alter, impose, discontinue, or waive any purchase fee, redemption fee, account service fee, or other fees charged to a shareholder or a group of shareholders; and (6) redeem an account or suspend account privileges, without the owner’s permission to do so, in cases of threatening conduct or activity Vanguard believes to be suspicious, fraudulent, or illegal. Changes may affect any or all investors. These actions will be taken when, at the sole discretion of Vanguard management, Vanguard reasonably believes they are in the best interest of a fund.

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Share Classes

Vanguard reserves the right, without notice, to change the eligibility requirements of its share classes, including the types of clients who are eligible to purchase each share class.

Fund and Account Updates

Confirmation Statements

We will send (or provide through our website, whichever you prefer) a confirmation of your trade date and the amount of your transaction when you buy, sell, exchange, or convert shares. However, we will not send confirmations reflecting only checkwriting redemptions or the reinvestment of dividend or capital gains distributions. For any month in which you had a checkwriting redemption, a Checkwriting Activity Statement will be sent to you itemizing the checkwriting redemptions for that month. Promptly review each confirmation statement that we provide to you. It is important that you contact Vanguard immediately with any questions you may have about any transaction reflected on a confirmation statement, or Vanguard will consider the transaction properly processed.

Portfolio Summaries

We will send (or provide through our website, whichever you prefer) quarterly portfolio summaries to help you keep track of your accounts throughout the year. Each summary shows the market value of your account at the close of the statement period, as well as all distributions, purchases, redemptions, exchanges, transfers, and conversions for the current calendar quarter (or month). Promptly review each summary that we provide to you. It is important that you contact Vanguard immediately with any questions you may have about any transaction reflected on the summary, or Vanguard will consider the transaction properly processed.

Tax Information Statements

For most accounts, Vanguard (or your intermediary) is required to provide annual tax forms to assist you in preparing your income tax returns. These forms are generally available for each calendar year early in the following year. Registered users of vanguard.com can also view certain forms through our website. Vanguard (or your intermediary) may also provide you with additional tax-related documentation. For more information, consult our website at vanguard.com or see Contacting Vanguard.

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Annual and Semiannual Reports

We will send (or provide through our website, whichever you prefer) reports about Vanguard Money Market Funds twice a year, in April and October. These reports include overviews of the financial markets and provide the following specific Fund information:

• Performance assessments and comparisons with industry benchmarks.
• Reports from the advisor.
• Financial statements with listings of Fund holdings.

Portfolio Holdings

Please consult the Funds‘ Statement of Additional Information or our website for a description of the policies and procedures that govern disclosure of a Fund’s portfolio holdings.

Employer-Sponsored Plans

Your plan administrator or your employee benefits office can provide you with detailed information on how to participate in your plan and how to elect a Fund as an investment option.

• If you have any questions about a Fund or Vanguard, including those about a Fund’s investment objective, strategies, or risks, contact Vanguard Participant Services toll-free at 800-523-1188 or visit our website at vanguard.com.

• If you have questions about your account, contact your plan administrator or the organization that provides recordkeeping services for your plan.

• Be sure to carefully read each topic that pertains to your transactions with Vanguard.

Vanguard reserves the right to change its policies without notice to shareholders.

Transactions

Processing times for your transaction requests may differ among recordkeepers or among transaction and funding types. Your plan’s recordkeeper (which may also be Vanguard) will determine the necessary processing time frames for your transaction requests prior to submission to a Fund. Consult your recordkeeper or plan administrator for more information.

If Vanguard is serving as your plan recordkeeper and if your transaction involves one or more investments with an early cut-off time for processing or another trading restriction, your entire transaction will be subject to the restriction when the trade date for your transaction is determined.

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Vanguard Addresses

Please be sure to use the correct address and the correct form. Use of an incorrect address or form could delay the processing of your transaction.

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Glossary of Investment Terms

Capital Gains Distributions. Payments to mutual fund shareholders of gains realized on securities that a fund has sold at a profit, minus any realized losses.

Cash Equivalent Investments. Cash deposits, short-term bank deposits, and money market instruments that include U.S. Treasury bills and notes, bank certificates of deposit (CDs), repurchase agreements, commercial paper, and banker’s acceptances.

Citigroup 3-Month U.S. Treasury Bill Index. An index that measures performance of short-term U.S. government debt securities and accrues income on a monthly basis.

Dividend Distributions. Payments to mutual fund shareholders of income from interest or dividends generated by a fund’s investments.

Expense Ratio. A fund’s total annual operating expenses expressed as a percentage of the fund’s average net assets. The expense ratio includes management and administrative expenses, but it does not include the transaction costs of buying and selling portfolio securities.

Inception Date. The date on which the assets of a fund (or one of its share classes) are first invested in accordance with the fund’s investment objective. For funds with a subscription period, the inception date is the day after that period ends. Investment performance is generally measured from the inception date.

Joint Committed Credit Facility. Each Fund participates, along with other funds managed by Vanguard, in a committed credit facility provided by a syndicate of lenders pursuant to a credit agreement that may be renewed annually; each Vanguard fund is individually liable for its borrowings, if any, under the credit facility. The amount and terms of the committed credit facility are subject to approval by the Funds’ board of trustees and renegotiation with the lender syndicate on an annual basis.

Money Market Instruments. Short-term, liquid investments (usually with a maturity of 397 days or less) that include U.S. Treasury bills and notes, bank certificates of deposit (CDs), repurchase agreements, commercial paper, and banker’s acceptances.

Mutual Fund. An investment company that pools the money of many people and invests it in a variety of securities in an effort to achieve a specific objective over time.

New York Stock Exchange (NYSE). A stock exchange based in New York City that is open for regular trading on business days, Monday through Friday, from 9:30 a.m. to 4 p.m., Eastern time. Net asset values (NAVs) are calculated each business day as of the close of regular trading on the NYSE.

Principal. The face value of a debt instrument or the amount of money put into an investment.

Securities. Stocks, bonds, money market instruments, and other investments.

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Stable Net Asset Value (NAV). A share price that maintains a consistent value (e.g., $1.00 or $100.00) using special pricing and valuation conventions.

Total Return. A percentage change, over a specified time period, in a mutual fund’s net asset value, assuming the reinvestment of all distributions of dividends and capital gains.

Volatility. The fluctuations in value of a mutual fund or other security. The greater a fund’s volatility, the wider the fluctuations in its returns.

Yield. Income (interest or dividends) earned by an investment, expressed as a percentage of the investment’s price.

Vanguard S&P Mid-Cap 400 Index Fund

Investment Objective

The Fund seeks to track the performance of a benchmark index that measures the investment return of mid-capitalization stocks in the United States.

Fees and Expenses

The following table describes the fees and expenses you may pay if you buy and hold Institutional Shares of the Fund.

The following example is intended to help you compare the cost of investing in the Fund’s Institutional Shares with the cost of investing in other mutual funds. It illustrates the hypothetical expenses that you would incur over various periods if you were to invest $10,000 in the Fund’s shares. This example assumes that the shares provide a return of 5% each year and that total annual fund operating expenses remain as stated in the preceding table. You would incur these hypothetical expenses whether or not you redeem your investment at the end of the given period. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

1

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in more taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the previous expense example, reduce the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 12% of the average value of its portfolio.

Principal Investment Strategies

The Fund employs an indexing investment approach designed to track the performance of the S&P MidCap 400^® Index. The Index measures the performance of mid-capitalization stocks in the United States. The Fund attempts to replicate the target index by investing all, or substantially all, of its assets in the stocks that make up the Index, holding each stock in approximately the same proportion as its weighting in the Index.

Principal Risks

An investment in the Fund could lose money over short or long periods of time. You should expect the Fund’s share price and total return to fluctuate within a wide range. The Fund is subject to the following risks, which could affect the Fund’s performance:

• Stock market risk, which is the chance that stock prices overall will decline. Stock markets tend to move in cycles, with periods of rising prices and periods of falling prices. The Fund’s target index tracks a subset of the U.S. stock market, which could cause the Fund to perform differently from the overall stock market. In addition, the Fund’s target index may, at times, become focused in stocks of a particular market sector, which would subject the Fund to proportionately higher exposure to the risks of that sector.

• Investment style risk, which is the chance that returns from mid-capitalization stocks will trail returns from the overall stock market. Historically, mid-cap stocks have been more volatile in price than the large-cap stocks that dominate the overall market, and they often perform quite differently. Mid-size companies tend to have greater stock volatility because, among other things, these companies tend to be more sensitive to changing economic conditions.

An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

2

Annual Total Returns

The following bar chart and table are intended to help you understand the risks of investing in the Fund. The bar chart shows how the performance of the Fund‘s Institutional Shares has varied from one calendar year to another over the periods shown. The table shows how the average annual total returns of the Institutional Shares compare with those of the Fund‘s target index, which has investment characteristics similar to those of the Fund. Keep in mind that the Fund’s past performance (before and after taxes) does not indicate how the Fund will perform in the future. Updated performance information is available on our website at vanguard.com/performance or by calling Vanguard toll-free at 800-662-7447.

Annual Total Returns — Vanguard S&P Mid-Cap 400 Index Fund Institutional Shares¹

1 The year-to-date return as of the most recent calendar quarter, which ended on September 30, 2018, was 7.43%.

During the periods shown in the bar chart, the highest return for a calendar quarter was 13.48% (quarter ended March 31, 2012), and the lowest return for a quarter was –8.52% (quarter ended September 30, 2015).

3

Actual after-tax returns depend on your tax situation and may differ from those shown in the preceding table. When after-tax returns are calculated, it is assumed that the shareholder was in the highest individual federal marginal income tax bracket at the time of each distribution of income or capital gains or upon redemption. State and local income taxes are not reflected in the calculations. Please note that after-tax returns are not relevant for a shareholder who holds fund shares in a tax-deferred account, such as an individual retirement account or a 401(k) plan. Also, figures captioned Return After Taxes on Distributions and Sale of Fund Shares may be higher than other figures for the same period if a capital loss occurs upon redemption and results in an assumed tax deduction for the shareholder.

Investment Advisor
The Vanguard Group, Inc. (Vanguard)

Portfolio Managers

William Coleman, CFA, Portfolio Manager at Vanguard. He has co-managed the Fund since 2015.

Awais Khan, CFA, Portfolio Manager at Vanguard. He has co-managed the Fund since 2017.

Purchase and Sale of Fund Shares

You may purchase or redeem shares online through our website (vanguard.com), by mail (The Vanguard Group, P.O. Box 1110, Valley Forge, PA 19482-1110), or by telephone (800-662-2739). The minimum investment amount required to open and maintain a Fund account for Institutional Shares is $5 million. The minimum investment amount required to add to an existing Fund account is generally $1. If you are investing through an employer-sponsored retirement or savings plan, your plan administrator or your benefits office can provide you with detailed information on how you can invest through your plan.

Tax Information

The Fund’s distributions may be taxable as ordinary income or capital gain. If you are investing through a tax-advantaged account, such as an IRA or an employer-sponsored retirement or savings plan, special tax rules apply.

Payments to Financial Intermediaries

The Fund and its investment advisor do not pay financial intermediaries for sales of Fund shares.

4

Vanguard S&P Mid-Cap 400 Value Index Fund

Investment Objective

The Fund seeks to track the performance of a benchmark index that measures the investment return of mid-capitalization value stocks in the United States.

Fees and Expenses

The following table describes the fees and expenses you may pay if you buy and hold Institutional Shares of the Fund.

The following example is intended to help you compare the cost of investing in the Fund’s Institutional Shares with the cost of investing in other mutual funds. It illustrates the hypothetical expenses that you would incur over various periods if you were to invest $10,000 in the Fund’s shares. This example assumes that the shares provide a return of 5% each year and that total annual fund operating expenses remain as stated in the preceding table. You would incur these hypothetical expenses whether or not you redeem your investment at the end of the given period. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

5

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in more taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the previous expense example, reduce the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 36% of the average value of its portfolio.

Principal Investment Strategies

The Fund employs an indexing investment approach designed to track the performance of the S&P MidCap 400^® Value Index, which represents the value companies, as determined by the index sponsor, of the S&P MidCap 400 Index. The Index measures the performance of mid-capitalization value stocks in the United States. The Fund attempts to replicate the target index by investing all, or substantially all, of its assets in the stocks that make up the Index, holding each stock in approximately the same proportion as its weighting in the Index.

Principal Risks

An investment in the Fund could lose money over short or long periods of time. You should expect the Fund’s share price and total return to fluctuate within a wide range. The Fund is subject to the following risks, which could affect the Fund’s performance:

• Stock market risk, which is the chance that stock prices overall will decline. Stock markets tend to move in cycles, with periods of rising prices and periods of falling prices. The Fund’s target index tracks a subset of the U.S. stock market, which could cause the Fund to perform differently from the overall stock market. In addition, the Fund’s target index may, at times, become focused in stocks of a particular market sector, which would subject the Fund to proportionately higher exposure to the risks of that sector.

• Investment style risk, which is the chance that returns from mid-capitalization value stocks will trail returns from the overall stock market. Historically, mid-cap stocks have been more volatile in price than the large-cap stocks that dominate the overall market, and they often perform quite differently. Mid-size companies tend to have greater stock volatility because, among other things, these companies tend to be more sensitive to changing economic conditions.

An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

6

Annual Total Returns

The following bar chart and table are intended to help you understand the risks of investing in the Fund. The bar chart shows how the performance of the Fund‘s Institutional Shares has varied from one calendar year to another over the periods shown. The table shows how the average annual total returns of the Institutional Shares compare with those of the Fund‘s target index, which has investment characteristics similar to those of the Fund. Keep in mind that the Fund’s past performance (before and after taxes) does not indicate how the Fund will perform in the future. Updated performance information is available on our website at vanguard.com/performance or by calling Vanguard toll-free at 800-662-7447.

Annual Total Returns — Vanguard S&P Mid-Cap 400 Value Index Fund Institutional Shares¹

1 The year-to-date return as of the most recent calendar quarter, which ended on September 30, 2018, was 5.99%.

During the periods shown in the bar chart, the highest return for a calendar quarter was 15.83% (quarter ended December 31, 2011), and the lowest return for a quarter was –20.95% (quarter ended September 30, 2011).

7

Actual after-tax returns depend on your tax situation and may differ from those shown in the preceding table. When after-tax returns are calculated, it is assumed that the shareholder was in the highest individual federal marginal income tax bracket at the time of each distribution of income or capital gains or upon redemption. State and local income taxes are not reflected in the calculations. Please note that after-tax returns are not relevant for a shareholder who holds fund shares in a tax-deferred account, such as an individual retirement account or a 401(k) plan. Also, figures captioned Return After Taxes on Distributions and Sale of Fund Shares may be higher than other figures for the same period if a capital loss occurs upon redemption and results in an assumed tax deduction for the shareholder.

Investment Advisor
The Vanguard Group, Inc. (Vanguard)

Portfolio Managers

William Coleman, CFA, Portfolio Manager at Vanguard. He has co-managed the Fund since 2015.

Awais Khan, CFA, Portfolio Manager at Vanguard. He has co-managed the Fund since 2017.

Purchase and Sale of Fund Shares

You may purchase or redeem shares online through our website (vanguard.com), by mail (The Vanguard Group, P.O. Box 1110, Valley Forge, PA 19482-1110), or by telephone (800-662-2739). The minimum investment amount required to open and maintain a Fund account for Institutional Shares is $5 million. The minimum investment amount required to add to an existing Fund account is generally $1. If you are investing through an employer-sponsored retirement or savings plan, your plan administrator or your benefits office can provide you with detailed information on how you can invest through your plan.

Tax Information

The Fund’s distributions may be taxable as ordinary income or capital gain. If you are investing through a tax-advantaged account, such as an IRA or an employer-sponsored retirement or savings plan, special tax rules apply.

Payments to Financial Intermediaries

The Fund and its investment advisor do not pay financial intermediaries for sales of Fund shares.

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Vanguard S&P Mid-Cap 400 Growth Index Fund

Investment Objective

The Fund seeks to track the performance of a benchmark index that measures the investment return of mid-capitalization growth stocks in the United States.

Fees and Expenses

The following table describes the fees and expenses you may pay if you buy and hold Institutional Shares of the Fund.

The following example is intended to help you compare the cost of investing in the Fund’s Institutional Shares with the cost of investing in other mutual funds. It illustrates the hypothetical expenses that you would incur over various periods if you were to invest $10,000 in the Fund’s shares. This example assumes that the shares provide a return of 5% each year and that total annual fund operating expenses remain as stated in the preceding table. You would incur these hypothetical expenses whether or not you redeem your investment at the end of the given period. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

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Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in more taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the previous expense example, reduce the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 43% of the average value of its portfolio.

Principal Investment Strategies

The Fund employs an indexing investment approach designed to track the performance of the S&P MidCap 400^® Growth Index, which represents the growth companies, as determined by the index sponsor, of the S&P MidCap 400 Index. The Index measures the performance of mid-capitalization growth stocks in the United States. The Fund attempts to replicate the target index by investing all, or substantially all, of its assets in the stocks that make up the Index, holding each stock in approximately the same proportion as its weighting in the Index.

Principal Risks

An investment in the Fund could lose money over short or long periods of time. You should expect the Fund’s share price and total return to fluctuate within a wide range. The Fund is subject to the following risks, which could affect the Fund’s performance:

• Stock market risk, which is the chance that stock prices overall will decline. Stock markets tend to move in cycles, with periods of rising prices and periods of falling prices. The Fund’s target index tracks a subset of the U.S. stock market, which could cause the Fund to perform differently from the overall stock market. In addition, the Fund’s target index may, at times, become focused in stocks of a particular market sector, which would subject the Fund to proportionately higher exposure to the risks of that sector.

• Investment style risk, which is the chance that returns from mid-capitalization growth stocks will trail returns from the overall stock market. Historically, mid-cap stocks have been more volatile in price than the large-cap stocks that dominate the overall market, and they often perform quite differently. Mid-size companies tend to have greater stock volatility because, among other things, these companies tend to be more sensitive to changing economic conditions.

An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

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Annual Total Returns

The following bar chart and table are intended to help you understand the risks of investing in the Fund. The bar chart shows how the performance of the Fund‘s Institutional Shares has varied from one calendar year to another over the periods shown. The table shows how the average annual total returns of the Institutional Shares compare with those of the Fund‘s target index, which has investment characteristics similar to those of the Fund. Keep in mind that the Fund’s past performance (before and after taxes) does not indicate how the Fund will perform in the future. Updated performance information is available on our website at vanguard.com/performance or by calling Vanguard toll-free at 800-662-7447.

Annual Total Returns — Vanguard S&P Mid-Cap 400 Growth Index Fund Institutional Shares¹

1 The year-to-date return as of the most recent calendar quarter, which ended on September 30, 2018, was 8.80%.

During the periods shown in the bar chart, the highest return for a calendar quarter was 14.07% (quarter ended March 31, 2012), and the lowest return for a quarter was –6.97% (quarter ended September 30, 2015).

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Actual after-tax returns depend on your tax situation and may differ from those shown in the preceding table. When after-tax returns are calculated, it is assumed that the shareholder was in the highest individual federal marginal income tax bracket at the time of each distribution of income or capital gains or upon redemption. State and local income taxes are not reflected in the calculations. Please note that after-tax returns are not relevant for a shareholder who holds fund shares in a tax-deferred account, such as an individual retirement account or a 401(k) plan. Also, figures captioned Return After Taxes on Distributions and Sale of Fund Shares may be higher than other figures for the same period if a capital loss occurs upon redemption and results in an assumed tax deduction for the shareholder.

Investment Advisor
The Vanguard Group, Inc. (Vanguard)

Portfolio Managers

William Coleman, CFA, Portfolio Manager at Vanguard. He has co-managed the Fund since 2015.

Awais Khan, CFA, Portfolio Manager at Vanguard. He has co-managed the Fund since 2017.

Purchase and Sale of Fund Shares

You may purchase or redeem shares online through our website (vanguard.com), by mail (The Vanguard Group, P.O. Box 1110, Valley Forge, PA 19482-1110), or by telephone (800-662-2739). The minimum investment amount required to open and maintain a Fund account for Institutional Shares is $5 million. The minimum investment amount required to add to an existing Fund account is generally $1. If you are investing through an employer-sponsored retirement or savings plan, your plan administrator or your benefits office can provide you with detailed information on how you can invest through your plan.

Tax Information

The Fund’s distributions may be taxable as ordinary income or capital gain. If you are investing through a tax-advantaged account, such as an IRA or an employer-sponsored retirement or savings plan, special tax rules apply.

Payments to Financial Intermediaries

The Fund and its investment advisor do not pay financial intermediaries for sales of Fund shares.

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Investing in Index Funds

What Is Indexing?

Indexing is an investment strategy for tracking the performance of a specified market benchmark, or “index.” An index is a group of securities whose overall performance is used as a standard to measure the investment performance of a particular market. There are many types of indexes. Some represent entire markets—such as the U.S. stock market or the U.S. bond market. Other indexes cover market segments—such as small-capitalization stocks or short-term bonds. One cannot invest directly in an index.

The index sponsor determines the securities to include in the index, the weighting of each security in the index, and the appropriate time to make changes to the composition of the index. Generally, the index sponsor does not provide any warranty, or accept any liability, with respect to the quality, accuracy, or completeness of either the target index or its related data. Errors made by the index sponsor may occur from time to time and Vanguard does not provide any warranty or guarantee against such errors. Therefore, the gains, losses, or costs associated with the index sponsor’s errors will generally be borne by the index fund and its shareholders.

An index fund seeks to hold all, or a representative sample, of the securities that make up its target index. Index funds attempt to mirror the performance of the target index, for better or worse. However, an index fund generally does not perform exactly like its target index. For example, index funds have operating expenses and transaction costs. Market indexes do not, and therefore they will usually have a slight performance advantage over funds that track them.

Index funds typically have the following characteristics:

• Variety of investments. Index funds generally invest in the securities of a variety of companies and industries.

• Relative performance consistency. Because they seek to track market benchmarks, index funds usually do not perform dramatically better or worse than their benchmarks.

• Low cost. Index funds are generally inexpensive to run compared with actively managed funds. They have low or no research costs and typically keep trading activity—and thus brokerage commissions and other transaction costs—to a minimum compared with actively managed funds.

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More on the Funds

This prospectus describes the principal risks you would face as a Fund shareholder. It is important to keep in mind one of the main principles of investing: generally, the higher the risk of losing money, the higher the potential reward. The reverse, also, is generally true: the lower the risk, the lower the potential reward. As you consider an investment in any mutual fund, you should take into account your personal tolerance for fluctuations in the securities markets. Look for this symbol throughout the prospectus. It is used to mark detailed information about the more significant risks that you would confront as a Fund shareholder. To highlight terms and concepts important to mutual fund investors, we have provided Plain Talk® explanations along the way. Reading the prospectus will help you decide whether a Fund is the right investment for you. We suggest that you keep this prospectus for future reference.

Share Class Overview

This prospectus offers the Funds‘ Institutional Shares, which are generally for investors who invest a minimum of $5 million. Each Fund also issues ETF Shares (an exchange-traded class of shares), which are offered through a separate prospectus.

Both share classes offered by a Fund have the same investment objective, strategies, and policies. However, different share classes have different expenses; as a result, their investment returns will differ.

The following sections explain the principal investment strategies and policies that each Fund uses in pursuit of its objective. The Funds‘ board of trustees, which oversees each Fund‘s management, may change investment strategies or policies in the interest of shareholders without a shareholder vote, unless those strategies or policies are designated as fundamental. Note that each Fund‘s investment objective is not fundamental and may be changed without a shareholder vote. Under normal circumstances, each Fund will invest at least 80% of its assets in the stocks that make up its target index. A Fund may change its 80% policy only upon 60 days‘ notice to shareholders.

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Market Exposure

Each Fund is subject to stock market risk, which is the chance that stock prices overall will decline. Stock markets tend to move in cycles, with periods of rising prices and periods of falling prices. Each Fund‘s target index tracks a subset of the U.S. stock market, which could cause the Fund to perform differently from the overall stock market. In addition, each Fund‘s target index may, at times, become focused in stocks of a particular market sector, which would subject the Fund to proportionately higher exposure to the risks of that sector.

To illustrate the volatility of stock prices, the following table shows the best, worst, and average annual total returns over various periods for the S&P 500 Index, a widely used barometer of U.S. stock market activity. Total returns consist of dividend income plus any change in market price. Note that the returns shown do not include the costs of buying and selling stocks or other expenses that real-world investment portfolios, such as the Funds, would incur.

The table covers all of the rolling 1-, 5-, 10-, and 20-year periods from 1926 through 2017. You can see, for example, that although the average annual return on common stocks for all of the 5-year periods was 10.1%, average annual returns for individual 5-year periods ranged from –12.4% (from 1928 through 1932) to 28.6% (from 1995 through 1999). These average annual returns reflect past performance of the S&P 500 Index; you should not regard them as an indication of future performance of either the U.S. stock market as a whole or the Funds in particular.

Keep in mind that the S&P 500 Index tracks mainly large-cap stocks. Historically, mid-cap stocks (such as those held by the Funds) have been more volatile than—and at times have performed quite differently from—the large-cap stocks of the S&P 500 Index.

Similarly, indexes that focus on growth stocks or value stocks will not necessarily perform in the same way as the broader S&P 500 Index. Both growth and value stocks have the potential at times to be more volatile than the broader markets.

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Stocks of publicly traded companies are often classified according to market capitalization, which is the market value of a company’s outstanding shares. These classifications typically include small-cap, mid-cap, and large-cap. It is important to understand that there are no “official” definitions of small-, mid-, and large-cap, even among Vanguard fund advisors, and that market capitalization ranges can change over time.

The asset-weighted median market capitalization of each Fund’s stock holdings as of August 31, 2018, was:

Each Fund is subject to investment style risk, which is the chance that returns from the types of stocks in which the Fund invests will trail returns from the overall stock market. Historically, mid-cap stocks have been more volatile in price than the large-cap stocks that dominate the overall market, and they often perform quite differently. Mid-size companies tend to have greater stock volatility because, among other things, these companies tend to be more sensitive to changing economic conditions.

Plain Talk About Growth Funds and Value Funds

Growth investing and value investing are two styles employed by stock-fund managers. Growth funds generally invest in stocks of companies believed to have above-average potential for growth in revenue, earnings, cash flow, or other similar criteria. These stocks typically have low dividend yields, if any, and above-average prices in relation to measures such as earnings and book value. Value funds typically invest in stocks whose prices are below average in relation to those measures; these stocks often have above-average dividend yields. Value stocks also may remain undervalued by the market for long periods of time. Growth and value stocks have historically produced similar long-term returns, though each style has periods when it outperforms the other.

Security Selection

Each Fund attempts to track the investment performance of a benchmark index that measures the return of a particular market segment. The Funds use the replication method of indexing, meaning that each Fund generally holds the same stocks as its target index and in approximately the same proportions.

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Other Investment Policies and Risks

Each Fund reserves the right to substitute a different index for the index it currently tracks if the current index is discontinued, if the Fund‘s agreement with the sponsor of its target index is terminated, or for any other reason determined in good faith by the Fund’s board of trustees. In any such instance, the substitute index would represent the same market segment as the current index.

Each Fund may invest in foreign securities to the extent necessary to carry out its investment strategy of holding all, or substantially all, of the stocks that make up the index it tracks. It is not expected that any Fund will invest more than 5% of its assets in foreign securities.

To track their target indexes as closely as possible, the Funds attempt to remain fully invested in stocks. To help stay fully invested and to reduce transaction costs, the Funds may invest, to a limited extent, in derivatives, including equity futures. The Funds may also use derivatives such as total return swaps to obtain exposure to a stock, a basket of stocks, or an index. Generally speaking, a derivative is a financial contract whose value is based on the value of a financial asset (such as a stock, a bond, or a currency), a physical asset (such as gold, oil, or wheat), a market index, or a reference rate. Investments in derivatives may subject the Funds to risks different from, and possibly greater than, those of investments directly in the underlying securities or assets. The Funds will not use derivatives for speculation or for the purpose of leveraging (magnifying) investment returns.

Cash Management

Each Fund‘s daily cash balance may be invested in Vanguard Market Liquidity Fund and/or Vanguard Municipal Cash Management Fund (the CMT Funds), which are low-cost money market funds. When investing in a Vanguard CMT Fund, each Fund bears its proportionate share of the expenses of the CMT Fund in which it invests. Vanguard receives no additional revenue from Fund assets invested in a Vanguard CMT Fund.

Methods Used to Meet Redemption Requests

Under normal circumstances, each Fund typically expects to meet redemptions with positive cash flows. When this is not an option, each Fund seeks to maintain its risk exposure by selling a cross section of the Fund’s holdings to meet redemptions, while also factoring in transaction costs. Additionally, a Fund may work with larger clients to implement their redemptions in a manner that is least disruptive to the portfolio; see “Potentially disruptive redemptions” under Redeeming Shares in the Investing With Vanguard section.

Under certain circumstances, including under stressed market conditions, there are additional tools that each Fund may use in order to meet redemptions, including advancing the settlement of market trades with counterparties to match investor

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redemption payments or delaying settlement of an investor’s transaction to match trade settlement within regulatory requirements. A Fund may also suspend payment of redemption proceeds for up to seven days; see “Emergency circumstances” under Redeeming Shares in the Investing With Vanguard section. Additionally under these unusual circumstances, a Fund may borrow money (subject to certain regulatory conditions and if available under board-approved procedures) through an interfund lending facility or through a bank line-of-credit, including a joint committed credit facility, in order to meet redemption requests.

Temporary Investment Measures

Each Fund may temporarily depart from its normal investment policies and strategies when the advisor believes that doing so is in the Fund‘s best interest, so long as the strategy or policy employed is consistent with the Fund‘s investment objective. For instance, the Fund may invest beyond its normal limits in derivatives or exchange-traded funds that are consistent with the Fund‘s investment objective when those instruments are more favorably priced or provide needed liquidity, as might be the case when the Fund receives large cash flows that it cannot prudently invest immediately.

Frequent Trading or Market-Timing

Background. Some investors try to profit from strategies involving frequent trading of mutual fund shares, such as market-timing. For funds holding foreign securities, investors may try to take advantage of an anticipated difference between the price of the fund’s shares and price movements in overseas markets, a practice also known as time-zone arbitrage. Investors also may try to engage in frequent trading of funds holding investments such as small-cap stocks and high-yield bonds. As money is shifted into and out of a fund by a shareholder engaging in frequent trading, the fund incurs costs for buying and selling securities, resulting in increased brokerage and administrative costs. These costs are borne by all fund shareholders, including the long-term investors who do not generate the costs. In addition, frequent trading may interfere with an advisor’s ability to efficiently manage the fund.

Policies to address frequent trading. The Vanguard funds (other than money market funds and short-term bond funds, but including Vanguard Short-Term Inflation-Protected Securities Index Fund) do not knowingly accommodate frequent trading. The board of trustees of each Vanguard fund (other than money market funds and short-term bond funds, but including Vanguard Short-Term Inflation-Protected Securities Index Fund) has adopted policies and procedures reasonably designed to detect and discourage frequent trading and, in some cases, to compensate the fund for the costs associated with it. These policies and procedures do not apply to ETF Shares because frequent trading in ETF Shares generally does not disrupt portfolio management or otherwise harm fund shareholders. Although there is no assurance that Vanguard will

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be able to detect or prevent frequent trading or market-timing in all circumstances, the following policies have been adopted to address these issues:

• Each Vanguard fund reserves the right to reject any purchase request—including exchanges from other Vanguard funds—without notice and regardless of size. For example, a purchase request could be rejected because the investor has a history of frequent trading or if Vanguard determines that such purchase may negatively affect a fund’s operation or performance.

• Each Vanguard fund (other than money market funds and short-term bond funds, but including Vanguard Short-Term Inflation-Protected Securities Index Fund) generally prohibits, except as otherwise noted in the Investing With Vanguard section, an investor’s purchases or exchanges into a fund account for 30 calendar days after the investor has redeemed or exchanged out of that fund account.

• Certain Vanguard funds charge shareholders purchase and/or redemption fees on transactions.

See the Investing With Vanguard section of this prospectus for further details on Vanguard’s transaction policies.

Each Vanguard fund (other than retail and government money market funds), in determining its net asset value, will use fair-value pricing when appropriate, as described in the Share Price section. Fair-value pricing may reduce or eliminate the profitability of certain frequent-trading strategies.

Do not invest with Vanguard if you are a market-timer.

Turnover Rate

Although the Funds generally seek to invest for the long term, each Fund may sell securities regardless of how long they have been held. Generally, an index fund sells securities in response to redemption requests from shareholders of conventional (not exchange-traded) shares or to changes in the composition of its target index. Turnover rates for mid-cap and small-cap stock index funds tend to be higher than for large-cap stock index funds (although still relatively low, compared with actively managed stock funds) because the indexes they track are more likely to change as a result of companies merging, growing, or failing. The Financial Highlights section of this prospectus shows historical turnover rates for each Fund. A turnover rate of 100%, for example, would mean that a Fund had sold and replaced securities valued at 100% of its net assets within a one-year period.

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Plain Talk About Turnover Rate

Before investing in a mutual fund, you should review its turnover rate. This rate gives an indication of how transaction costs, which are not included in the fund’s expense ratio, could affect the fund’s future returns. In general, the greater the volume of buying and selling by the fund, the greater the impact that brokerage commissions and other transaction costs will have on its return. Also, funds with high turnover rates may be more likely to generate capital gains, including short-term capital gains, that must be distributed to shareholders and will be taxable to shareholders investing through a taxable account.

The Funds and Vanguard

Each Fund is a member of The Vanguard Group, a family of over 200 funds holding assets of approximately $4.9 trillion. All of the funds that are members of The Vanguard Group (other than funds of funds) share in the expenses associated with administrative services and business operations, such as personnel, office space, and equipment.

Vanguard Marketing Corporation provides marketing services to the funds. Although fund shareholders do not pay sales commissions or 12b-1 distribution fees, each fund (other than a fund of funds) or each share class of a fund (in the case of a fund with multiple share classes) pays its allocated share of the Vanguard funds’ marketing costs.

Plain Talk About Vanguard’s Unique Corporate Structure

The Vanguard Group is owned jointly by the funds it oversees and thus indirectly by the shareholders in those funds. Most other mutual funds are operated by management companies that are owned by third parties—either public or private stockholders—not by the funds they serve.

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Investment Advisor

The Vanguard Group, Inc., P.O. Box 2600, Valley Forge, PA 19482, which began operations in 1975, serves as advisor to the Funds through its Equity Index Group. As of August 31, 2018, Vanguard served as advisor for approximately $4.2 trillion in assets. Vanguard provides investment advisory services to the Funds pursuant to the Funds’ Service Agreement and subject to the supervision and oversight of the trustees and officers of the Funds.

For the fiscal year ended August 31, 2018, the advisory expenses represented an effective annual rate of 0.01% for the S&P Mid-Cap 400 Index and S&P Mid-Cap 400 Growth Index Funds, and 0.02% for the S&P Mid-Cap 400 Value Index Fund.

Under the terms of an SEC exemption, the Funds‘ board of trustees may, without prior approval from shareholders, change the terms of an advisory agreement with a third-party investment advisor or hire a new third-party investment advisor—either as a replacement for an existing advisor or as an additional advisor. Any significant change in a Fund’s advisory arrangements will be communicated to shareholders in writing. As the Funds‘ sponsor and overall manager, Vanguard may provide investment advisory services to a Fund at any time. Vanguard may also recommend to the board of trustees that an advisor be hired, terminated, or replaced or that the terms of an existing advisory agreement be revised. The Funds have filed an application seeking a similar SEC exemption with respect to investment advisors that are wholly owned subsidiaries of Vanguard. If the exemption is granted, the Funds may rely on the new SEC relief.

For a discussion of why the board of trustees approved each Fund’s investment advisory arrangement, see the most recent annual report to shareholders covering the fiscal year ended August 31.

The managers primarily responsible for the day-to-day management of the Funds are:

William Coleman, CFA, Portfolio Manager at Vanguard. He has worked in investment management since joining Vanguard in 2006 and has co-managed the S&P Mid-Cap 400 Index, S&P Mid-Cap 400 Value Index, and S&P Mid-Cap 400 Growth Index Funds since 2015. Education: B.S., King’s College; M.S., Saint Joseph’s University.

Awais Khan, CFA, Portfolio Manager at Vanguard. He has been with Vanguard since 2010; has worked in investment management since 2012; and has co-managed the S&P Mid-Cap 400 Index, S&P Mid-Cap 400 Value Index, and S&P Mid-Cap 400 Growth Index Funds since 2017. Education: B.S./B.S.B.A., University of North Carolina.

The Statement of Additional Information provides information about each portfolio manager’s compensation, other accounts under management, and ownership of shares of the Funds.

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Dividends, Capital Gains, and Taxes

Fund Distributions

Each Fund distributes to shareholders virtually all of its net income (interest and dividends, less expenses) as well as any net short-term or long-term capital gains realized from the sale of its holdings. Income dividends for the S&P Mid-Cap 400 Index Fund generally are distributed quarterly in March, June, September, and December; income dividends for the S&P Mid-Cap 400 Value Index and S&P Mid-Cap 400 Growth Index Funds generally are distributed annually in December. Capital gains distributions, if any, generally occur annually in December. In addition, each Fund may occasionally make a supplemental distribution at some other time during the year.

You can receive distributions of income or capital gains in cash, or you can have them automatically reinvested in more shares of the Fund. However, if you are investing through an employer-sponsored retirement or savings plan, your distributions will be automatically reinvested in additional Fund shares.

Plain Talk About Distributions

As a shareholder, you are entitled to your portion of a fund’s income from interest and dividends as well as capital gains from the fund’s sale of investments. Income consists of both the dividends that the fund earns from any stock holdings and the interest it receives from any money market and bond investments. Capital gains are realized whenever the fund sells securities for higher prices than it paid for them. These capital gains are either short-term or long-term, depending on whether the fund held the securities for one year or less or for more than one year.

Basic Tax Points

Investors in taxable accounts should be aware of the following basic federal income tax points:

• Distributions are taxable to you whether or not you reinvest these amounts in additional Fund shares.

• Distributions declared in December—if paid to you by the end of January—are taxable as if received in December.

• Any dividend distribution or short-term capital gains distribution that you receive is taxable to you as ordinary income. If you are an individual and meet certain holding-period requirements with respect to your Fund shares, you may be eligible for reduced tax rates on “qualified dividend income,” if any, distributed by the Fund.

• Any distribution of net long-term capital gains is taxable to you as long-term capital gains, no matter how long you have owned shares in the Fund.

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• Capital gains distributions may vary considerably from year to year as a result of the Funds‘ normal investment activities and cash flows.

• A sale or exchange of Fund shares is a taxable event. This means that you may have
• capital gain to report as income, or a capital loss to report as a deduction, when you

complete your tax return.

• Any conversion between classes of shares of the same fund is a nontaxable event. By contrast, an exchange between classes of shares of different funds is a taxable event.

• Vanguard (or your intermediary) will send you a statement each year showing the tax status of all of your distributions.

Individuals, trusts, and estates whose income exceeds certain threshold amounts are subject to a 3.8% Medicare contribution tax on “net investment income.” Net investment income takes into account distributions paid by the Fund and capital gains from any sale or exchange of Fund shares.

Dividend distributions and capital gains distributions that you receive, as well as your gains or losses from any sale or exchange of Fund shares, may be subject to state and local income taxes.

This prospectus provides general tax information only. If you are investing through a tax-advantaged account, such as an IRA or an employer-sponsored retirement or savings plan, special tax rules apply. Please consult your tax advisor for detailed information about any tax consequences for you.

Plain Talk About Buying a Dividend

Unless you are a tax-exempt investor or investing through a tax-advantaged account (such as an IRA or an employer-sponsored retirement or savings plan), you should consider avoiding a purchase of fund shares shortly before the fund makes a distribution, because doing so can cost you money in taxes. This is known as “buying a dividend.” For example: On December 15, you invest $5,000, buying 250 shares for $20 each. If the fund pays a distribution of $1 per share on December 16, its share price will drop to $19 (not counting market change). You still have only $5,000 (250 shares x $19 = $4,750 in share value, plus 250 shares x $1 = $250 in distributions), but you owe tax on the $250 distribution you received—even if you reinvest it in more shares. To avoid buying a dividend, check a fund’s distribution schedule before you invest.

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General Information

Backup withholding. By law, Vanguard must withhold 24% of any taxable distributions or redemptions from your account if you do not:

• Provide your correct taxpayer identification number.
• Certify that the taxpayer identification number is correct.
• Confirm that you are not subject to backup withholding.

Similarly, Vanguard (or your intermediary) must withhold taxes from your account if the IRS instructs us to do so.

Foreign investors. Vanguard funds offered for sale in the United States (Vanguard U.S. funds), including the Funds offered in this prospectus, are not widely available outside the United States. Non-U.S. investors should be aware that U.S. withholding and estate taxes and certain U.S. tax reporting requirements may apply to any investments in Vanguard U.S. funds. Foreign investors should visit the Non-U.S. investors page on our website at vanguard.com for information on Vanguard’s non-U.S. products.

Invalid addresses. If a dividend distribution or capital gains distribution check mailed to your address of record is returned as undeliverable, Vanguard will automatically reinvest the distribution and all future distributions until you provide us with a valid mailing address. Reinvestments will receive the net asset value calculated on the date of the reinvestment.

Share Price

Share price, also known as net asset value (NAV), is calculated each business day as of the close of regular trading on the New York Stock Exchange (NYSE), generally 4 p.m., Eastern time. In the rare event the NYSE experiences unanticipated disruptions and is unavailable at the close of the trading day, NAVs will be calculated as of the close of regular trading on the Nasdaq (or another alternate exchange if the Nasdaq is unavailable, as determined at Vanguard’s discretion), generally 4 p.m., Eastern time. Each share class has its own NAV, which is computed by dividing the total assets, minus liabilities, allocated to the share class by the number of Fund shares outstanding for that class. On U.S. holidays or other days when the NYSE is closed, the NAV is not calculated, and the Funds do not sell or redeem shares. However, on those days the value of a Fund’s assets may be affected to the extent that the Fund holds securities that change in value on those days (such as foreign securities that trade on foreign markets that are open).

Stocks held by a Vanguard fund are valued at their market value when reliable market quotations are readily available from the principal exchange or market on which they are traded. Such securities are generally valued at their official closing price, the last

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reported sales price, or if there were no sales that day, the mean between the closing bid and asking prices. When a fund determines that market quotations either are not readily available or do not accurately reflect the value of a security, the security is priced at its fair value (the amount that the owner might reasonably expect to receive upon the current sale of the security).

The values of any foreign securities held by a fund are converted into U.S. dollars using an exchange rate obtained from an independent third party as of the close of regular trading on the NYSE. The values of any mutual fund shares, including institutional money market fund shares, held by a fund are based on the NAVs of the shares. The values of any ETF shares or closed-end fund shares held by a fund are based on the market value of the shares.

A fund also will use fair-value pricing if the value of a security it holds has been materially affected by events occurring before the fund’s pricing time but after the close of the principal exchange or market on which the security is traded. This most commonly occurs with foreign securities, which may trade on foreign exchanges that close many hours before the fund’s pricing time. Intervening events might be company-specific (e.g., earnings report, merger announcement) or country-specific or regional/global (e.g., natural disaster, economic or political news, act of terrorism, interest rate change). Intervening events include price movements in U.S. markets that exceed a specified threshold or that are otherwise deemed to affect the value of foreign securities.

Fair-value pricing may be used for domestic securities—for example, if (1) trading in a security is halted and does not resume before the fund’s pricing time or a security does not trade in the course of a day and (2) the fund holds enough of the security that its price could affect the NAV.

Fair-value prices are determined by Vanguard according to procedures adopted by the board of trustees. When fair-value pricing is employed, the prices of securities used by a fund to calculate the NAV may differ from quoted or published prices for the same securities.

Vanguard fund share prices are published daily on our website at vanguard.com/prices.

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Financial Highlights

The following financial highlights tables are intended to help you understand each Fund’s financial performance for the periods shown, and certain information reflects financial results for a single Fund share. The total returns in each table represent the rate that an investor would have earned or lost each period on an investment in the Fund (assuming reinvestment of all distributions). This information has been obtained from the financial statements audited by PricewaterhouseCoopers LLP, an independent registered public accounting firm, whose report—along with each Fund’s financial statements—is included in the Funds‘ most recent annual report to shareholders. You may obtain a free copy of the latest annual or semiannual report by visiting vanguard.com or by contacting Vanguard by telephone or mail.

1 Calculated based on average shares outstanding.

2 Excludes the value of portfolio securities received or delivered as a result of in-kind purchases or redemptions of the Fund’s capital shares, including ETF Creation Units.

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1 Calculated based on average shares outstanding.

2 Excludes the value of portfolio securities received or delivered as a result of in-kind purchases or redemptions of the Fund’s capital shares, including ETF Creation Units.

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1 Calculated based on average shares outstanding.

2 Excludes the value of portfolio securities received or delivered as a result of in-kind purchases or redemptions of the Fund’s capital shares, including ETF Creation Units.

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Investing With Vanguard

This section of the prospectus explains the basics of doing business with Vanguard. Vanguard fund shares can be held directly with Vanguard or indirectly through an intermediary, such as a bank, a broker, or an investment advisor. If you hold Vanguard fund shares directly with Vanguard, you should carefully read each topic within this section that pertains to your relationship with Vanguard. If you hold Vanguard fund shares indirectly through an intermediary (including shares held in a brokerage account through Vanguard Brokerage Services^®), please see Investing With Vanguard Through Other Firms, and also refer to your account agreement with the intermediary for information about transacting in that account. If you hold Vanguard fund shares through an employer-sponsored retirement or savings plan, please see Employer-Sponsored Plans. Vanguard reserves the right to change the following policies without notice. Please call or check online for current information. See Contacting Vanguard.

For Vanguard fund shares held directly with Vanguard, each fund you hold in an account is a separate “fund account.” For example, if you hold three funds in a nonretirement account titled in your own name, two funds in a nonretirement account titled jointly with your spouse, and one fund in an individual retirement account, you have six fund accounts—and this is true even if you hold the same fund in multiple accounts. Note that each reference to “you” in this prospectus applies to any one or more registered account owners or persons authorized to transact on your account.

Purchasing Shares

Vanguard reserves the right, without notice, to increase or decrease the minimum amount required to open, convert shares to, or maintain a fund account or to add to an existing fund account.

Investment minimums may differ for certain categories of investors.

Account Minimums for Institutional Shares To open and maintain an account. $5 million.

Certain Vanguard institutional clients may meet the minimum investment amount by aggregating separate accounts within the same Fund. This aggregation policy does not apply to financial intermediaries.

Vanguard may charge additional recordkeeping fees for institutional clients whose accounts are recordkept by Vanguard. Please contact your Vanguard representative to determine whether additional recordkeeping fees apply to your account.

To add to an existing account. Generally $1.

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How to Initiate a Purchase Request

Be sure to check Exchanging Shares, Frequent-Trading Limitations, and Other Rules You Should Know before placing your purchase request.

Online. You may open certain types of accounts, request a purchase of shares, and request an exchange through our website or our mobile application if you are registered for online access.

By telephone. You may call Vanguard to begin the account registration process or request that the account-opening forms be sent to you. You may also call Vanguard to request a purchase of shares in your account or to request an exchange. See

Contacting Vanguard.

By mail. You may send Vanguard your account registration form and check to open a new fund account. To add to an existing fund account, you may send your check with an Invest-by-Mail form (from a transaction confirmation or your account statement) or with a deposit slip (available online). For a list of Vanguard addresses, see Contacting Vanguard.

How to Pay for a Purchase

By electronic bank transfer. You may purchase shares of a Vanguard fund through an electronic transfer of money from a bank account. To establish the electronic bank transfer service on an account, you must designate the bank account online, complete a form, or fill out the appropriate section of your account registration form. After the service is set up on your account, you can purchase shares by electronic bank transfer on a regular schedule (Automatic Investment Plan) or upon request. Your purchase request can be initiated online (if you are registered for online access), by telephone, or by mail.

By wire. Wiring instructions vary for different types of purchases. Please call Vanguard for instructions and policies on purchasing shares by wire. See Contacting Vanguard.

By check. You may make initial or additional purchases to your fund account by sending a check with a deposit slip or by utilizing our mobile application if you are registered for online access. Also see How to Initiate a Purchase Request. Make your check payable to Vanguard and include the appropriate fund number (e.g., Vanguard—xx). For a list of Fund numbers (for Funds in this prospectus), see Additional Information.

By exchange. You may purchase shares of a Vanguard fund using the proceeds from the simultaneous redemption of shares of another Vanguard fund. You may initiate an exchange online (if you are registered for online access), by telephone, or by mail with an exchange form. See Exchanging Shares.

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Trade Date

The trade date for any purchase request received in good order will depend on the day and time Vanguard receives your request, the manner in which you are paying, and the type of fund you are purchasing. Your purchase will be executed using the NAV as calculated on the trade date. NAVs are calculated only on days that the NYSE is open for trading (a business day).

For purchases by check into all funds other than money market funds and for purchases by exchange, wire, or electronic bank transfer (not using an Automatic Investment Plan) into all funds: If the purchase request is received by Vanguard on a business day before the close of regular trading on the NYSE (generally 4 p.m., Eastern time), the trade date for the purchase will be the same day. If the purchase request is received on a business day after the close of regular trading on the NYSE, or on a nonbusiness day, the trade date for the purchase will be the next business day.

For purchases by check into money market funds: If the purchase request is received by Vanguard on a business day before the close of regular trading on the NYSE (generally 4 p.m., Eastern time), the trade date for the purchase will be the next business day. If the purchase request is received on a business day after the close of regular trading on the NYSE, or on a nonbusiness day, the trade date for the purchase will be the second business day following the day Vanguard receives the purchase request. Because money market instruments must be purchased with federal funds and it takes a money market mutual fund one business day to convert check proceeds into federal funds, the trade date for the purchase will be one business day later than for other funds.

For purchases by electronic bank transfer using an Automatic Investment Plan: Your trade date generally will be the date you selected for withdrawal of funds from your designated bank account. Your bank account generally will be debited on the business day after your trade date. If the date you selected for withdrawal of funds from your bank account falls on a weekend, holiday, or other nonbusiness day, your trade date generally will be the previous business day. For retirement accounts, if the date you selected for withdrawal of funds from your designated bank account falls on the last business day of the year, your trade date will be the first business day of the following year. Please note that if you select the first of the month for automated withdrawals from your designated bank account, trades designated for January 1 will receive the next business day’s trade date.

If your purchase request is not accurate and complete, it may be rejected. See Other Rules You Should Know—Good Order.

For further information about purchase transactions, consult our website at vanguard.com or see Contacting Vanguard.

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Other Purchase Rules You Should Know

Check purchases. All purchase checks must be written in U.S. dollars and must be drawn on a U.S. bank and be accompanied by good order instructions. Vanguard does not accept cash, traveler’s checks, starter checks, or money orders. In addition, Vanguard may refuse checks that are not made payable to Vanguard.

New accounts. We are required by law to obtain from you certain personal information that we will use to verify your identity. If you do not provide the information, we may not be able to open your account. If we are unable to verify your identity, Vanguard reserves the right, without notice, to close your account or take such other steps as we deem reasonable. Certain types of accounts may require additional documentation.

Refused or rejected purchase requests. Vanguard reserves the right to stop selling fund shares or to reject any purchase request at any time and without notice, including, but not limited to, purchases requested by exchange from another Vanguard fund. This also includes the right to reject any purchase request because the investor has a history of frequent trading or because the purchase may negatively affect a fund’s operation or performance.

Large purchases. Call Vanguard before attempting to invest a large dollar amount.

No cancellations. Vanguard will not accept your request to cancel any purchase request once processing has begun. Please be careful when placing a purchase request.

Converting Shares

If you convert from Institutional Shares to ETF Shares, the transaction will be based on the respective NAVs of the separate share classes on the trade date of the conversion.

Vanguard will not accept your request to cancel any self-directed conversion request once processing has begun. Please be careful when placing a conversion request.

A conversion between share classes of the same fund is a nontaxable event.

Conversions to ETF Shares

Owners of conventional shares (i.e., not exchange-traded shares) issued by a Fund may convert those shares to ETF Shares of equivalent value of the same fund. Please note that investors who own conventional shares through a 401(k) plan or other employer-sponsored retirement or benefit plan generally may not convert those shares to ETF Shares and should check with their plan sponsor or recordkeeper. ETF Shares, whether acquired through a conversion or purchased on the secondary market, cannot be converted to conventional shares by a shareholder. Also, ETF Shares of one fund cannot be exchanged for ETF Shares of another fund.

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ETF Shares must be held in a brokerage account. Thus, before converting conventional shares to ETF Shares, you must have an existing, or open a new, brokerage account. This account may be with Vanguard Brokerage Services or with any other brokerage firm.

Vanguard Brokerage Services does not impose a fee on conversions from conventional shares to Vanguard ETF Shares. However, other brokerage firms may charge a fee to process a conversion. Vanguard reserves the right, in the future, to impose a transaction fee on conversions or to limit, temporarily suspend, or terminate the conversion privilege. For additional information on converting conventional shares to ETF Shares, please contact Vanguard to obtain a prospectus for ETF Shares. See

Contacting Vanguard.

Redeeming Shares

How to Initiate a Redemption Request

Be sure to check Exchanging Shares, Frequent-Trading Limitations, and Other Rules You Should Know before placing your redemption request.

Online. You may request a redemption of shares or request an exchange through our website or our mobile application if you are registered for online access.

By telephone. You may call Vanguard to request a redemption of shares or an exchange. See Contacting Vanguard.

By mail. You may send a form (available online) to Vanguard to redeem from a fund account or to make an exchange. See Contacting Vanguard.

How to Receive Redemption Proceeds

By electronic bank transfer. You may have the proceeds of a fund redemption sent directly to a designated bank account. To establish the electronic bank transfer service on an account, you must designate a bank account online, complete a special form, or fill out the appropriate section of your account registration form. After the service is set up on your account, you can redeem shares by electronic bank transfer on a regular schedule (Automatic Withdrawal Plan) or upon request. Your redemption request can be initiated online (if you are registered for online access), by telephone, or by mail.

By wire. To receive your proceeds by wire, you may instruct Vanguard to wire your redemption proceeds ($100 minimum) to a previously designated bank account. To establish the wire redemption service, you generally must designate a bank account online, complete a special form, or fill out the appropriate section of your account registration form.

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Please note that Vanguard charges a $10 wire fee for outgoing wire redemptions. The fee is assessed in addition to, rather than being withheld from, redemption proceeds and is paid directly to the fund. For example, if you redeem $100 via a wire, you will receive the full $100, and your fund account will also be assessed the $10 fee by redeeming additional fund shares. If you redeem your entire fund account, your redemption proceeds will be reduced by the fee amount. The wire fee does not apply to accounts held by Flagship and Flagship Select clients; accounts held through intermediaries, including Vanguard Brokerage Services; or accounts held by institutional clients.

By exchange. You may have the proceeds of a Vanguard fund redemption invested directly in shares of another Vanguard fund. You may initiate an exchange online (if you are registered for online access), by telephone, or by mail. See Exchanging Shares.

By check. If you have not chosen another redemption method, Vanguard will mail you a redemption check, generally payable to all registered account owners, normally within two business days of your trade date, and generally to the address of record.

Trade Date

The trade date for any redemption request received in good order will depend on the day and time Vanguard receives your request and the manner in which you are redeeming. Your redemption will be executed using the NAV as calculated on the trade date. NAVs are calculated only on days that the NYSE is open for trading (a business day).

For redemptions by check, exchange, or wire: If the redemption request is received by Vanguard on a business day before the close of regular trading on the NYSE (generally 4 p.m., Eastern time), the trade date will be the same day. If the redemption request is received on a business day after the close of regular trading on the NYSE, or on a nonbusiness day, the trade date will be the next business day.

• Note on timing of wire redemptions from money market funds: For telephone requests received by Vanguard on a business day before 10:45 a.m., Eastern time (2 p.m., Eastern time, for Vanguard Prime Money Market Fund; 12:30 p.m., Eastern time, for Vanguard Federal Money Market Fund), the redemption proceeds generally will leave Vanguard by the close of business the same day. For telephone requests received by Vanguard on a business day after those cut-off times, or on a nonbusiness day, and for all requests other than by telephone, the redemption proceeds generally will leave Vanguard by the close of business on the next business day.

• Note on timing of wire redemptions from all other funds: For requests received by Vanguard on a business day before the close of regular trading on the NYSE (generally 4 p.m., Eastern time), the redemption proceeds generally will leave

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Vanguard by the close of business on the next business day. For requests received by Vanguard on a business day after the close of regular trading on the NYSE, or on a nonbusiness day, the redemption proceeds generally will leave Vanguard by the close of business on the second business day after Vanguard receives the request.

For redemptions by electronic bank transfer using an Automatic Withdrawal Plan: Your trade date generally will be the date you selected for withdrawal of funds (redemption of shares) from your Vanguard account. Proceeds of redeemed shares generally will be credited to your designated bank account two business days after your trade date. If the date you selected for withdrawal of funds from your Vanguard account falls on a weekend, holiday, or other nonbusiness day, your trade date generally will be the previous business day. For retirement accounts, if the date you selected for withdrawal of funds from your Vanguard account falls on the last day of the year and if that date is a holiday, your trade date will be the first business day of the following year. Please note that if you designate the first of the month for automated withdrawals, trades designated for January 1 will receive the next business day’s trade date.

For redemptions by electronic bank transfer not using an Automatic Withdrawal Plan: If the redemption request is received by Vanguard on a business day before the close of regular trading on the NYSE (generally 4 p.m., Eastern time), the trade date will be the same day. If the redemption request is received on a business day after the close of regular trading on the NYSE, or on a nonbusiness day, the trade date will be the next business day.

If your redemption request is not accurate and complete, it may be rejected. If we are unable to send your redemption proceeds by wire or electronic bank transfer because the receiving institution rejects the transfer, Vanguard will make additional efforts to complete your transaction. If Vanguard is still unable to complete the transaction, we may send the proceeds of the redemption to you by check, generally payable to all registered account owners, or use your proceeds to purchase new shares of the fund from which you sold shares for the purpose of the wire or electronic bank transfer transaction. See Other Rules You Should Know—Good Order.

If your redemption request is received in good order, we typically expect that redemption proceeds will be paid by a Fund within one business day of the trade date; however, in certain circumstances, investors may experience a longer settlement period at the time of the transaction. For further information, see “Potentially disruptive redemptions” and “Emergency circumstances.”

For further information about redemption transactions, consult our website at vanguard.com or see Contacting Vanguard.

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Other Redemption Rules You Should Know

Documentation for certain accounts. Special documentation may be required to redeem from certain types of accounts, such as trust, corporate, nonprofit, or retirement accounts. Please call us before attempting to redeem from these types of accounts.

Potentially disruptive redemptions. Vanguard reserves the right to pay all or part of a redemption in kind—that is, in the form of securities—if we reasonably believe that a cash redemption would negatively affect the fund’s operation or performance or that the shareholder may be engaged in market-timing or frequent trading. Under these circumstances, Vanguard also reserves the right to delay payment of the redemption proceeds for up to seven calendar days. By calling us before you attempt to redeem a large dollar amount, you may avoid in-kind or delayed payment of your redemption. Please see Frequent-Trading Limitations for information about Vanguard’s policies to limit frequent trading.

Recently purchased shares. Although you can redeem shares at any time, proceeds may not be made available to you until the fund collects payment for your purchase. This may take up to seven calendar days for shares purchased by check or by electronic bank transfer. If you have written a check on a fund with checkwriting privileges, that check may be rejected if your fund account does not have a sufficient available balance.

Address change. If you change your address online or by telephone, there may be up to a 15-day restriction on your ability to request check redemptions online and by telephone. You can request a redemption in writing (using a form available online) at any time. Confirmations of address changes are sent to both the old and new addresses.

Payment to a different person or address. At your request, we can make your redemption check payable, or wire your redemption proceeds, to a different person or send it to a different address. However, this generally requires the written consent of all registered account owners and may require additional documentation, such as a signature guarantee or a notarized signature. You may obtain a signature guarantee from some commercial or savings banks, credit unions, trust companies, or member firms of a U.S. stock exchange.

No cancellations. Vanguard will not accept your request to cancel any redemption request once processing has begun. Please be careful when placing a redemption request.

Emergency circumstances. Vanguard funds can postpone payment of redemption proceeds for up to seven calendar days. In addition, Vanguard funds can suspend redemptions and/or postpone payments of redemption proceeds beyond seven calendar days at times when the NYSE is closed or during emergency circumstances, as determined by the SEC.

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Exchanging Shares

An exchange occurs when you use the proceeds from the redemption of shares of one Vanguard fund to simultaneously purchase shares of a different Vanguard fund. You can make exchange requests online (if you are registered for online access), by telephone, or by mail. See Purchasing Shares and Redeeming Shares.

If the NYSE is open for regular trading (generally until 4 p.m., Eastern time, on a business day) at the time an exchange request is received in good order, the trade date generally will be the same day. See Other Rules You Should Know—Good Order for additional information on all transaction requests.

Vanguard will not accept your request to cancel any exchange request once processing has begun. Please be careful when placing an exchange request.

Call Vanguard before attempting to exchange a large dollar amount. By calling us before you attempt to exchange a large dollar amount, you may avoid delayed or rejected transactions.

Please note that Vanguard reserves the right, without notice, to revise or terminate the exchange privilege, limit the amount of any exchange, or reject an exchange, at any time, for any reason. See Frequent-Trading Limitations for additional restrictions on exchanges.

Frequent-Trading Limitations

Because excessive transactions can disrupt management of a fund and increase the fund’s costs for all shareholders, the board of trustees of each Vanguard fund places certain limits on frequent trading in the funds. Each Vanguard fund (other than money market funds and short-term bond funds, but including Vanguard Short-Term Inflation-Protected Securities Index Fund) limits an investor’s purchases or exchanges into a fund account for 30 calendar days after the investor has redeemed or exchanged out of that fund account. ETF Shares are not subject to these frequent-trading limits.

For Vanguard Retirement Investment Program pooled plans, the limitations apply to exchanges made online or by telephone.

These frequent-trading limitations do not apply to the following:

• Purchases of shares with reinvested dividend or capital gains distributions.
• Transactions through Vanguard’s Automatic Investment Plan, Automatic Exchange

Service, Direct Deposit Service, Automatic Withdrawal Plan, Required Minimum Distribution Service, and Vanguard Small Business Online^®.

• Discretionary transactions through Vanguard Asset Management Services^™, Vanguard Personal Advisor Services^®, and Vanguard Institutional Advisory Services^®.

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• Redemptions of shares to pay fund or account fees.
• Redemptions of shares to remove excess shareholder contributions to certain

types of retirement accounts (including, but not limited to, IRAs, certain Individual 403(b)(7) Custodial Accounts, and Vanguard Individual 401(k) Plans).

• Transfers and reregistrations of shares within the same fund.
• Purchases of shares by asset transfer or direct rollover.
• Conversions of shares from one share class to another in the same fund.
• Checkwriting redemptions.
• Section 529 college savings plans.
• Certain approved institutional portfolios and asset allocation programs, as well as

trades made by funds or trusts managed by Vanguard or its affiliates that invest in other Vanguard funds. (Please note that shareholders of Vanguard’s funds of funds are subject to the limitations.)

For participants in employer-sponsored defined contribution plans,* the frequent-trading limitations do not apply to:

• Purchases of shares with participant payroll or employer contributions or loan repayments.

• Purchases of shares with reinvested dividend or capital gains distributions.
• Distributions, loans, and in-service withdrawals from a plan.
• Redemptions of shares as part of a plan termination or at the direction of the plan.
• Transactions executed through the Vanguard Managed Account Program.
• Redemptions of shares to pay fund or account fees.
• Share or asset transfers or rollovers.
• Reregistrations of shares.
• Conversions of shares from one share class to another in the same fund.
• Exchange requests submitted by written request to Vanguard. (Exchange requests

submitted by fax, if otherwise permitted, are subject to the limitations.)

* The following Vanguard fund accounts are subject to the frequent-trading limitations: SEP-IRAs, SIMPLE IRAs, certain Individual 403(b)(7) Custodial Accounts, and Vanguard Individual 401(k) Plans.

Accounts Held by Institutions (Other Than Defined Contribution Plans)

Vanguard will systematically monitor for frequent trading in institutional clients’ accounts. If we detect suspicious trading activity, we will investigate and take appropriate action, which may include applying to a client’s accounts the 30-day policy

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previously described, prohibiting a client’s purchases of fund shares, and/or revoking the client’s exchange privilege.

Accounts Held by Intermediaries

When intermediaries establish accounts in Vanguard funds for the benefit of their clients, we cannot always monitor the trading activity of the individual clients. However, we review trading activity at the intermediary (omnibus) level, and if we detect suspicious activity, we will investigate and take appropriate action. If necessary, Vanguard may prohibit additional purchases of fund shares by an intermediary, including for the benefit of certain of the intermediary’s clients. Intermediaries also may monitor their clients’ trading activities with respect to Vanguard funds.

For those Vanguard funds that charge purchase and/or redemption fees, intermediaries will be asked to assess these fees on client accounts and remit these fees to the funds. The application of purchase and redemption fees and frequent-trading limitations may vary among intermediaries. There are no assurances that Vanguard will successfully identify all intermediaries or that intermediaries will properly assess purchase and redemption fees or administer frequent-trading limitations. If you invest with Vanguard through an intermediary, please read that firm’s materials carefully to learn of any other rules or fees that may apply.

Other Rules You Should Know

Prospectus and Shareholder Report Mailings

When two or more shareholders have the same last name and address, just one summary prospectus (or prospectus) and/or shareholder report may be sent in an attempt to eliminate the unnecessary expense of duplicate mailings. You may request individual prospectuses and reports by contacting our Client Services Department in writing, by telephone, or online. See Contacting Vanguard.

Vanguard.com

Registration. If you are a registered user of vanguard.com, you can review your account holdings; buy, sell, or exchange shares of most Vanguard funds; and perform most other transactions through our website. You must register for this service online.

Electronic delivery. Vanguard can deliver your account statements, transaction confirmations, prospectuses, certain tax forms, and shareholder reports electronically. If you are a registered user of vanguard.com, you can consent to the electronic delivery of these documents by logging on and changing your mailing preferences under “Account Maintenance.” You can revoke your electronic consent at any time

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through our website, and we will begin to send paper copies of these documents within 30 days of receiving your revocation.

Telephone Transactions

Automatic. When we set up your account, we will automatically enable you to do business with us by telephone, unless you instruct us otherwise in writing.

Tele-Account^®. To obtain fund and account information through Vanguard’s automated telephone service, you must first establish a Personal Identification Number (PIN) by calling Tele-Account at 800-662-6273.

Proof of a caller’s authority. We reserve the right to refuse a telephone request if the caller is unable to provide the requested information or if we reasonably believe that the caller is not an individual authorized to act on the account. Before we allow a caller to act on an account, we may request the following information:

• Authorization to act on the account (as the account owner or by legal documentation or other means).

• Account registration and address.

• Fund name and account number, if applicable.

• Other information relating to the caller, the account owner, or the account.

Good Order

We reserve the right to reject any transaction instructions that are not in “good order.” Good order generally means that your instructions:

• Are provided by the person(s) authorized in accordance with Vanguard’s policies and procedures to access the account and request transactions.

• Include the fund name and account number.

• Include the amount of the transaction (stated in dollars, shares, or percentage).

Written instructions also must generally be provided on a Vanguard form and include:

• Signature(s) and date from the authorized person(s).

• Signature guarantees or notarized signatures, if required for the type of transaction.

(Call Vanguard for specific requirements.)

• Any supporting documentation that may be required.

The requirements for written instructions vary among types of accounts and transactions. For more information, consult our website at vanguard.com or see

Contacting Vanguard.

Vanguard reserves the right, without notice, to revise the requirements for good order.

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Future Trade-Date Requests

Vanguard does not accept requests to hold a purchase, conversion, redemption, or exchange transaction for a future date. All such requests will receive trade dates as previously described in Purchasing Shares, Converting Shares, Redeeming Shares, and

Exchanging Shares. Vanguard reserves the right to return future-dated purchase checks.

Accounts With More Than One Owner

If an account has more than one owner or authorized person, Vanguard generally will accept instructions from any one owner or authorized person.

Responsibility for Fraud

Vanguard will not be responsible for any account losses because of fraud if we reasonably believe that the person transacting business on an account is authorized to do so. Please take precautions to protect yourself from fraud. Keep your account information private, and immediately review any account statements or other information that we provide to you. It is important that you contact Vanguard immediately about any transactions or changes to your account that you believe to be unauthorized.

Uncashed Checks

Please cash your distribution or redemption checks promptly. Vanguard will not pay interest on uncashed checks. Vanguard may be required to transfer assets related to uncashed checks to a state under the state’s abandoned property law.

Dormant Accounts

If your account has no activity in it for a period of time, Vanguard may be required to transfer it to a state under the state’s abandoned property law, subject to potential federal or state withholding taxes.

Unusual Circumstances

If you experience difficulty contacting Vanguard online or by telephone, you can send us your transaction request on a Vanguard form by regular or express mail. See Contacting Vanguard for addresses.

Investing With Vanguard Through Other Firms

You may purchase or sell shares of most Vanguard funds through a financial intermediary, such as a bank, a broker, or an investment advisor. Please consult your financial intermediary to determine which, if any, shares are available through that firm and to learn about other rules that may apply. Your financial intermediary can provide you with account information and any required tax forms.

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Please see Frequent-Trading Limitations—Accounts Held by Intermediaries for information about the assessment of any purchase or redemption fees and the monitoring of frequent trading for accounts held by intermediaries.

Low-Balance Accounts

Each Fund reserves the right to liquidate a fund account whose balance falls below the account minimum for any reason, including market fluctuation. This liquidation policy applies to nonretirement fund accounts and accounts that are held through intermediaries. Any such liquidation will be preceded by written notice to the investor.

Right to Change Policies

In addition to the rights expressly stated elsewhere in this prospectus, Vanguard reserves the right, without notice, to (1) alter, add, or discontinue any conditions of purchase (including eligibility requirements), redemption, exchange, conversion, service, or privilege at any time; (2) accept initial purchases by telephone; (3) freeze any account and/or suspend account services if Vanguard has received reasonable notice of a dispute regarding the assets in an account, including notice of a dispute between the registered or beneficial account owners, or if Vanguard reasonably believes a fraudulent transaction may occur or has occurred; (4) temporarily freeze any account and/or suspend account services upon initial notification to Vanguard of the death of the shareholder until Vanguard receives required documentation in good order; (5) alter, impose, discontinue, or waive any purchase fee, redemption fee, account service fee, or other fees charged to a shareholder or a group of shareholders; and (6) redeem an account or suspend account privileges, without the owner’s permission to do so, in cases of threatening conduct or activity Vanguard believes to be suspicious, fraudulent, or illegal. Changes may affect any or all investors. These actions will be taken when, at the sole discretion of Vanguard management, Vanguard reasonably believes they are in the best interest of a fund.

Share Classes

Vanguard reserves the right, without notice, to change the eligibility requirements of its share classes, including the types of clients who are eligible to purchase each share class.

Fund and Account Updates

Confirmation Statements

We will send (or provide through our website, whichever you prefer) a confirmation of your trade date and the amount of your transaction when you buy, sell, exchange, or convert shares. However, we will not send confirmations reflecting only checkwriting

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redemptions or the reinvestment of dividend or capital gains distributions. For any month in which you had a checkwriting redemption, a Checkwriting Activity Statement will be sent to you itemizing the checkwriting redemptions for that month. Promptly review each confirmation statement that we provide to you. It is important that you contact Vanguard immediately with any questions you may have about any transaction reflected on a confirmation statement, or Vanguard will consider the transaction properly processed.

Portfolio Summaries

We will send (or provide through our website, whichever you prefer) quarterly portfolio summaries to help you keep track of your accounts throughout the year. Each summary shows the market value of your account at the close of the statement period, as well as all distributions, purchases, redemptions, exchanges, transfers, and conversions for the current calendar quarter (or month). Promptly review each summary that we provide to you. It is important that you contact Vanguard immediately with any questions you may have about any transaction reflected on the summary, or Vanguard will consider the transaction properly processed.

Tax Information Statements

For most accounts, Vanguard (or your intermediary) is required to provide annual tax forms to assist you in preparing your income tax returns. These forms are generally available for each calendar year early in the following year. Registered users of vanguard.com can also view certain forms through our website. Vanguard (or your intermediary) may also provide you with additional tax-related documentation. For more information, consult our website at vanguard.com or see Contacting Vanguard.

Annual and Semiannual Reports

We will send (or provide through our website, whichever you prefer) reports about Vanguard S&P Mid-Cap 400 Index Funds twice a year, in April and October. These reports include overviews of the financial markets and provide the following specific Fund information:

• Performance assessments and comparisons with industry benchmarks.
• Financial statements with listings of Fund holdings.

Portfolio Holdings

Please consult the Funds‘ Statement of Additional Information or our website for a description of the policies and procedures that govern disclosure of a Fund’s portfolio holdings.

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Employer-Sponsored Plans

Your plan administrator or your employee benefits office can provide you with detailed information on how to participate in your plan and how to elect a Fund as an investment option.

• If you have any questions about a Fund or Vanguard, including those about a Fund’s investment objective, strategies, or risks, contact Vanguard Participant Services toll-free at 800-523-1188 or visit our website at vanguard.com.

• If you have questions about your account, contact your plan administrator or the organization that provides recordkeeping services for your plan.

• Be sure to carefully read each topic that pertains to your transactions with Vanguard.

Vanguard reserves the right to change its policies without notice to shareholders.

Transactions

Processing times for your transaction requests may differ among recordkeepers or among transaction and funding types. Your plan’s recordkeeper (which may also be Vanguard) will determine the necessary processing time frames for your transaction requests prior to submission to a Fund. Consult your recordkeeper or plan administrator for more information.

If Vanguard is serving as your plan recordkeeper and if your transaction involves one or more investments with an early cut-off time for processing or another trading restriction, your entire transaction will be subject to the restriction when the trade date for your transaction is determined.

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