Vanguard Money Market Funds Prospectus Investor Shares

Vanguard Treasury Money Market Fund

Supplement Dated May 14, 2021, to the Prospectus and Summary Prospectus Dated December 22, 2020

The purpose of this supplement is to provide you with information regarding permissible investments for Vanguard Treasury Money Market Fund (the Fund).

As previously announced, the Board of Trustees of the Fund (the Board) approved permitting the Fund to invest in repurchase agreements with the Federal Reserve Bank of New York that are fully collateralized by U.S. Treasury securities (Fed Repo). The Fund will invest solely in U.S. Treasury securities and in Fed Repo.

Also as previously announced, in connection with this change, the Board approved modifying the Fund's policy to invest, under normal circumstances, at least 80% of its assets in U.S. Treasury securities. Under the revised policy, the Fund will invest, under normal circumstances, at least 80% of its assets in U.S. Treasury securities and in repurchase agreements fully collateralized by U.S. Treasury securities. Shareholders were provided with 60 days' notice of this change. The Fund's revised 80% policy is now effective.

The following changes are effective immediately.

Prospectus and Summary Prospectus Text Changes The following replaces similar language under the heading "Principal Investment Strategies" in the Vanguard Treasury Money Market Fund section:

The Fund invests solely in high-quality, short-term money market instruments 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 and in repurchase agreements fully collateralized by U.S. Treasury securities; the remainder of the assets will be invested in U.S. Treasury securities and in repurchase agreements fully collateralized by U.S. Treasury securities. The only repurchase agreements that the Fund will invest in are those with the Federal Reserve Bank of New York that are fully collateralized by U.S. Treasury securities. The Fund maintains a dollar-weighted average maturity of 60 days or less and a dollar-weighted average life of 120 days or less.

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

Prospectus Text Changes The following replaces similar language in the More on the Funds section:

Each 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. Each Fund's policy of investing at least 99.5% of its assets in government securities may be changed only upon 60 days' notice to shareholders. The Cash Reserves Federal Money Market Fund's and the Federal Money Market Fund's policies of investing at least 80% of their 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 and in repurchase agreements fully collateralized by U.S. Treasury securities also may be changed only upon 60 days' notice to shareholders.

The following replaces similar language under the heading "Security Selection" in the More on the Funds section:

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 and in repurchase agreements fully collateralized by U.S. Treasury securities. The remainder of the Fund's assets will be invested in U.S. Treasury securities and in repurchase agreements fully collateralized by U.S. Treasury securities.

Each Fund reserves the right to invest in repurchase agreements, which are subject to specific risks. The Treasury Money Market Fund will invest only in repurchase agreements with the Federal Reserve Bank of New York fully collateralized by U.S. Treasury securities. The Treasury Money Market Fund reserves the right to change this policy at any time and without prior notice to shareholders.

? 2021 The Vanguard Group, Inc. All rights reserved. Vanguard Marketing Corporation, Distributor.

PS 030S 052021

Vanguard Treasury Money Market Fund

Supplement Dated March 10, 2021, to the Prospectus Dated December 22, 2020

Prospectus Text Changes The following replaces the third paragraph under the heading "The Funds and Vanguard" in the More on the Funds section:

Vanguard and the Fund's Board have voluntarily agreed to temporarily limit certain net operating expenses for Vanguard Cash Reserves Federal Money Market Fund's Investor Shares and Admiral Shares in excess of their respective daily yields so as to maintain a zero or positive yield. Vanguard and the Funds' Boards have also voluntarily agreed to temporarily limit certain net operating expenses for each of Vanguard Federal Money Market Fund and Vanguard Treasury Money Market Fund in excess of each Fund's daily yield so as to maintain a zero or positive yield for the Fund. Vanguard and the Funds' Boards may terminate such temporary expense limitations at any time.

? 2021 The Vanguard Group, Inc. All rights reserved. Vanguard Marketing Corporation, Distributor.

PS 030Q 032021

Vanguard Cash Reserves Federal Money Market Fund

Vanguard Federal Money Market Fund

Supplement Dated January 25, 2021, to the Prospectus Dated December 22, 2020

Prospectus Text Changes The following replaces the third paragraph under the heading "The Funds and Vanguard" in the More on the Funds section:

Vanguard Cash Reserves Federal Money Market Fund and Federal Money Market Fund Only. Vanguard and the Funds' Board have voluntarily agreed to temporarily limit certain net operating expenses for the Vanguard Cash Reserves Federal Money Market Fund's Investor Shares and Admiral Shares in excess of their respective daily yields so as to maintain a zero or positive yield. Vanguard and the Funds' Board have also voluntarily agreed to temporarily limit certain net operating expenses for the Vanguard Federal Money Market Fund in excess of the Fund's daily yield so as to maintain a zero or positive yield for the Fund. Vanguard and the Funds' Board may terminate such temporary expense limitations at any time.

? 2021 The Vanguard Group, Inc. All rights reserved. Vanguard Marketing Corporation, Distributor.

PS 030N 012021

Vanguard Cash Reserves Federal Money Market Fund

Supplement Dated December 22, 2020, to the Prospectus and Summary Prospectus Dated December 22, 2020

Effective immediately, Investor Shares of Vanguard Cash Reserves Federal Money Market Fund (formerly known as Vanguard Prime Money Market Fund) are closed to new investors. The Fund's Investor Shares will remain open to existing investors. You may convert your Investor Shares of the Fund to Admiral Shares at any time by contacting Vanguard.

It is anticipated that all of the Fund's outstanding Investor Shares will be automatically converted to Admiral Shares beginning in the fourth quarter of 2020 and continuing through 2021. Once all outstanding shares are converted, the Investor share class will be eliminated.

? 2020 The Vanguard Group, Inc. All rights reserved. Vanguard Marketing Corporation, Distributor.

PS 030M 122020

Vanguard Money Market Funds Prospectus

December 22, 2020

Investor and AdmiralTM Shares Vanguard Cash Reserves Federal Money Market Fund Investor Shares* (VMMXX) Vanguard Cash Reserves Federal Money Market Fund Admiral Shares* (VMRXX) Vanguard Federal Money Market Fund Investor Shares (VMFXX) Vanguard Treasury Money Market Fund Investor Shares (VUSXX)

*Formerly known as Vanguard Prime Money Market Fund.

See the inside front cover for important information about access to your fund's annual and semiannual shareholder reports.

This prospectus contains financial data for the Funds through the fiscal year ended August 31, 2020. 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.

Important information about access to shareholder reports

Beginning on January 1, 2021, as permitted by regulations adopted by the SEC, paper copies of your fund's annual and semiannual shareholder reports will no longer be sent to you by mail, unless you specifically request them. Instead, you will be notified by mail each time a report is posted on the website and will be provided with a link to access the report.

If you have already elected to receive shareholder reports electronically, you will not be affected by this change and do not need to take any action. You may elect to receive shareholder reports and other communications from the fund electronically by contacting your financial intermediary (such as a broker-dealer or bank) or, if you invest directly with the fund, by calling Vanguard at one of the phone numbers on the back cover of this prospectus or by logging on to .

You may elect to receive paper copies of all future shareholder reports free of charge. If you invest through a financial intermediary, you can contact the intermediary to request that you continue to receive paper copies. If you invest directly with the fund, you can call Vanguard at one of the phone numbers on the back cover of this prospectus or log on to . Your election to receive paper copies will apply to all the funds you hold through an intermediary or directly with Vanguard.

Contents

Fund Summaries

Investing With Vanguard

35

Vanguard Cash Reserves Federal Money

Market Fund

1 Purchasing Shares

35

Vanguard Federal Money Market Fund

7 Converting Shares

38

Vanguard Treasury Money Market Fund

12 Redeeming Shares

39

Investing in Money Market Funds

16 Exchanging Shares

44

More on the Funds

18 Other Rules You Should Know

44

The Funds and Vanguard

26 Fund and Account Updates

49

Investment Advisor

26 Employer-Sponsored Plans

50

Dividends, Capital Gains, and Taxes

28 Contacting Vanguard

51

Share Price

29 Additional Information

52

Financial Highlights

31 Glossary of Investment Terms

53

Vanguard Cash Reserves 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, hold, and sell Investor Shares or Admiral Shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the table and example below.

Shareholder Fees (Fees paid directly from your investment)

Sales Charge (Load) Imposed on Purchases Purchase Fee Sales Charge (Load) Imposed on Reinvested Dividends Redemption Fee Account Service Fee Per Year (for certain fund account balances below $10,000)

Admiral Shares None None None None

$20

Investor Shares None None None None

$20

Annual Fund Operating Expenses (Expenses that you pay each year as a percentage of the value of your investment)

Management Fees 12b-1 Distribution Fee Other Expenses Total Annual Fund Operating Expenses

Admiral Shares 0.09% None 0.01% 0.10%

Investor Shares 0.14% None 0.02% 0.16%

1

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