Form 497 EATON VANCE INVESTMENT

EATON VANCE FLOATING-RATE MUNICIPAL INCOME FUND

Supplement to Prospectus dated August 1, 2021

Effective January 1, 2022, the following replaces “Restrictions on Excessive Trading and Market Timing.” under “Purchasing Shares”:

Restrictions on Excessive Trading and Market Timing. The Fund is not intended for excessive trading or market timing. Market timers seek to profit by rapidly switching money into a fund when they expect the share price of the fund to rise and taking money out of the fund when they expect those prices to fall. By realizing profits through short-term trading, shareholders that engage in rapid purchases and sales (including exchanges, if permitted) of a fund’s shares may dilute the value of shares held by long-term shareholders. Volatility resulting from excessive purchases and sales of fund shares, especially involving large dollar amounts, may disrupt efficient portfolio management. In particular, excessive purchases and sales of a fund’s shares may cause a fund to have difficulty implementing its investment strategies, may force the fund to sell portfolio securities at inopportune times to raise cash or may cause increased expenses (such as increased brokerage costs, realization of taxable capital gains without attaining any investment advantage or increased administrative costs).

A fund that invests in securities that are, among other things, thinly traded, traded infrequently or illiquid, is susceptible to the risk that the current market price for such securities may not accurately reflect current market values. A shareholder may seek to engage in short-term trading to take advantage of these pricing differences (commonly referred to as “price arbitrage”). The investment adviser is authorized to use the fair value of a security if prices are unavailable or are deemed unreliable (see “Valuing Shares”). The use of fair value pricing and the restrictions on excessive trading and market timing described below are intended to reduce a shareholder’s ability to engage in price arbitrage to the detriment of the Fund.

Notwithstanding the foregoing, a substantial portion of the Fund may be held by shareholders that have invested in the Fund as part of a short-term investment strategy. Shareholders employing such a strategy may purchase and redeem Fund shares frequently. Frequent trading may cause the Fund to experience high portfolio turnover, which may result in higher Fund transaction costs and realization of taxable capital gains for shareholders. The Boards of the Eaton Vance funds have adopted policies to discourage excessive trading and market timing and to seek to minimize their potentially detrimental effects (the “Policy”). Under the Policy, the Board has delegated to Eaton Vance Management, acting in its capacity as the Fund’s sub-transfer agent (“Eaton Vance”) the responsibility to reject or cancel a purchase order, suspend or terminate an exchange privilege or terminate the ability of a shareholder to invest in the Eaton Vance funds if Eaton Vance determines that a proposed transaction involves market timing or excessive trading that it believes is likely to be detrimental to the Fund. Eaton Vance has made a determination that transactions in the Fund are generally exempt from the Policy; however, Eaton Vance reserves the right to reject or cancel any purchase order (including an exchange) from a shareholder or group of shareholders for any reason.

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