VOOV Vanguard S&P 500 Value

Vanguard S&P Mid-Cap 400 Index Fund Summary Prospectus

December 20, 2019

Institutional Shares

Vanguard S&P Mid-Cap 400 Index Fund Institutional Shares (VSPMX)

The Fund's statutory Prospectus and Statement of Additional Information dated December 20, 2019, as may be amended or supplemented, are incorporated into and made part of this Summary Prospectus by reference.

Before you invest, you may want to review the Fund's Prospectus, which contains more information about the Fund and its risks. You can find the Fund's Prospectus and other information about the Fund online at www.vanguard.com/prospectus. You can also obtain this information at no cost by calling 800-662-7447 (if you are an individual investor) or 888-809-8102 (if you are a client of Vanguard's Institutional Division) or by sending an email request to online@vanguard.com.

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

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 vanguard.com.

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 vanguard.com. Your election to receive paper copies will apply to all the funds you hold through an intermediary or directly with Vanguard.

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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 the mid-capitalization 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. The stock prices of mid-size companies tend to experience greater 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.

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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.

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Vanguard S&P Mid-Cap 400 Index Fund Institutional Shares—Fund Number 1842

CFA® is a registered trademark owned by CFA Institute.

The S&P MidCap 400 Index (the "Index") is a product of S&P Dow Jones Indices LLC ("SPDJI"), and has been licensed for use by Vanguard. Standard & Poor's® and S&P® are registered trademarks of Standard & Poor's Financial Services LLC ("S&P"); Dow Jones® is a registered trademark of Dow Jones Trademark Holdings LLC ("Dow Jones"); S&P® and S&P 500® are trademarks of S&P and these trademarks have been licensed for use by SPDJI and sublicensed for certain purposes by Vanguard. Vanguard S&P Mid-Cap 400 Index Fund is not sponsored, endorsed, sold, or promoted by SPDJI, Dow Jones, S&P, or any of their respective affiliates (collectively, "S&P Dow Jones Indices"). S&P Dow Jones Indices makes no representation or warranty, express or implied, to the owners of Vanguard S&P Mid-Cap 400 Index Fund or any member of the public regarding the advisability of investing in securities generally or in Vanguard S&P Mid-Cap 400 Index Fund particularly or the ability of the S&P MidCap 400 Index to track general market performance. S&P Dow Jones Indices' only relationship to Vanguard with respect to the S&P MidCap 400 Index is the licensing of the Index and certain trademarks, service marks, and/ or trade names of S&P Dow Jones Indices and/or its licensors. The S&P MidCap 400 Index is determined, composed and calculated by S&P Dow Jones Indices without regard to Vanguard or Vanguard S&P Mid-Cap 400 Index Fund. S&P Dow Jones Indices has no obligation to take the needs of Vanguard or the owners of Vanguard S&P Mid-Cap 400 Index Fund into consideration in determining, composing, or calculating the S&P MidCap 400 Index. S&P Dow Jones Indices is not responsible for and has not participated in the determination of the prices, and amount of Vanguard S&P Mid-Cap 400 Index Fund or the timing of the issuance or sale of Vanguard S&P Mid-Cap 400 Index Fund or in the determination or calculation of the equation by which Vanguard S&P Mid-Cap 400 Index Fund is to be converted into cash, surrendered, or redeemed, as the case may be. S&P Dow Jones Indices has no obligation or liability in connection with the administration, marketing, or trading of Vanguard S&P Mid-Cap 400 Index Fund. There is no assurance that investment products based on the S&P MidCap 400 Index will accurately track index performance or provide positive investment returns. S&P Dow Jones Indices LLC is not an investment advisor. Inclusion of a security within an index is not a recommendation by S&P Dow Jones Indices to buy, sell, or hold such security, nor is it considered to be investment advice.

S&P DOW JONES INDICES DOES NOT GUARANTEE THE ADEQUACY, ACCURACY, TIMELINESS, AND/OR THE COMPLETENESS OF THE INDEX OR ANY DATA RELATED THERETO OR ANY COMMUNICATION, INCLUDING BUT NOT LIMITED TO, ORAL OR WRITTEN COMMUNICATION (INCLUDING ELECTRONIC COMMUNICATIONS) WITH RESPECT THERETO. S&P DOW JONES INDICES SHALL NOT BE SUBJECT TO ANY DAMAGES OR LIABILITY FOR ANY ERRORS, OMISSIONS, OR DELAYS THEREIN. S&P DOW JONES INDICES MAKES NO EXPRESS OR IMPLIED WARRANTIES, AND EXPRESSLY DISCLAIMS ALL WARRANTIES, OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE OR USE OR AS TO RESULTS TO BE OBTAINED BY VANGUARD, OWNERS OF VANGUARD S&P MID-CAP 400 INDEX FUND, OR ANY OTHER PERSON OR ENTITY FROM THE USE OF THE INDEX OR WITH RESPECT TO ANY DATA RELATED THERETO. WITHOUT LIMITING ANY OF THE FOREGOING, IN NO EVENT WHATSOEVER SHALL S&P DOW JONES INDICES BE LIABLE FOR ANY INDIRECT, SPECIAL, INCIDENTAL, PUNITIVE, OR CONSEQUENTIAL DAMAGES INCLUDING BUT NOT LIMITED TO, LOSS OF PROFITS, TRADING LOSSES, LOST TIME OR GOODWILL, EVEN IF THEY HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES, WHETHER IN CONTRACT, TORT, STRICT LIABILITY, OR OTHERWISE. THERE ARE NO THIRD PARTY BENEFICIARIES OF ANY AGREEMENTS OR ARRANGEMENTS BETWEEN S&P DOW JONES INDICES AND VANGUARD, OTHER THAN THE LICENSORS OF S&P DOW JONES INDICES.

To request additional information about the Fund, please visit vanguard.com or contact 800-662-7447

(if you are an individual investor) or 888-809-8102 (if you are a client of Vanguard's Institutional Division).

© 2019 The Vanguard Group, Inc. All rights reserved. Vanguard Marketing Corporation, Distributor.

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