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Vanguard Mega Cap Growth Index Fund Summary Prospectus

December 20, 2019

Institutional Shares

Vanguard Mega Cap Growth Index Fund Institutional Shares (VMGAX)

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.

Investment Objective

The Fund seeks to track the performance of a benchmark index that measures the investment return of large-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.

Shareholder Fees

(Fees paid directly from your investment)

Sales Charge (Load) Imposed on Purchases	None
Purchase Fee	None

Sales Charge (Load) Imposed on Reinvested Dividends	None

Redemption Fee	None

Annual Fund Operating Expenses

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

Management Fees	0.06%
12b-1 Distribution Fee	None

Other Expenses	0.00%

Total Annual Fund Operating Expenses	0.06%

Example

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 were to 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 Year	3 Years	5 Years	10 Years
$6	$19	$34	$77

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 14% of the average value of its portfolio.

Principal Investment Strategies

The Fund employs an indexing investment approach designed to track the performance of the CRSP US Mega Cap Growth Index, which represents the growth companies as determined by the index sponsor, of the CRSP US Mega Cap Index. The Index is a float-adjusted, market-capitalization-weighted index designed to measure equity market performance of mega-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. The Fund may become nondiversified, as defined under the Investment Company Act of 1940, solely as a result of a change in relative market capitalization or index weighting of one or more constituents of 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 large-capitalization growth stocks in which the Fund invests will trail returns from the overall stock market. Large-cap growth stocks tend to go through cycles of doing better—or worse—than other segments of the stock market or the stock market in general. These periods have, in the past, lasted for as long as several years.

•Nondiversification risk. Due to a recent index rebalance and in order to closely track the composition of the Fund's target index, more than 25% of the Fund's total assets are invested in issuers representing more than 5% of the Fund's total assets. As a result, the Fund is nondiversified under the Investment Company Act of 1940, although it continues to hold more than 100 stocks across a number of sectors. The Fund's performance may be hurt disproportionately by the poor performance of relatively few stocks, or even a single stock, and the Fund's shares may experience significant fluctuations in value.

•Sector risk, which is the chance that significant problems will affect a particular sector, or that returns from that sector will trail returns from the overall stock market. Daily fluctuations in specific market sectors are often more extreme or volatile than fluctuations in the overall market. Because a significant portion of the Fund's assets are invested in the information technology sector, the Fund's performance is impacted by the general condition of that sector. Companies in the information technology sector could be affected by, among other things, overall economic conditions, short product cycles, rapid obsolescence of products, competition, and government regulation. Sector risk is expected to be high for the Fund.

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.

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 and other comparative indexes, which have investment characteristics similar to those of the Fund. The Spliced Mega Cap Growth Index reflects the performance of the MSCI US Large Cap Growth Index through April 16, 2013, and the CRSP US Mega Cap Growth Index thereafter. 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 Mega Cap Growth Index Fund Institutional Shares1

	2009		2010	2011	2012	2013	2014	2015	2016	2017	2018
60%		35.10				32.48
60%
40%										29.49
20%			14.69	3.07	17.25		13.67	3.72	6.42
					17.25

0%
0%
-20%											-2.85
-20%
-40%
-40%

1 The year-to-date return as of the most recent calendar quarter, which ended on September 30, 2019, was 24.53%.

During the periods shown in the bar chart, the highest return for a calendar quarter was 15.27% (quarter ended June 30, 2009), and the lowest return for a quarter was –16.46% (quarter ended December 31, 2018).

Average Annual Total Returns for Periods Ended December 31, 2018

	1 Year	5 Years	10 Years
Vanguard Mega Cap Growth Index Fund Institutional Shares

Return Before Taxes	–2.85%	9.56%	14.62%

Return After Taxes on Distributions	–3.09	9.21	14.31

Return After Taxes on Distributions and Sale of Fund Shares	–1.49	7.53	12.34

Comparative Indexes
(reflect no deduction for fees, expenses, or taxes)

MSCI US Large Cap Growth Index	–1.39%	10.37%	15.10%

Spliced Mega Cap Growth Index	–2.85	9.61	14.71

CRSP US Mega Cap Growth Index	–2.85	9.61	—

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

Michael A. Johnson, Portfolio Manager at Vanguard. He has co-managed the Fund since 2015.

Gerard C. O'Reilly, Principal of Vanguard. He has co-managed the Fund since 2015.

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.

Vanguard Mega Cap Growth Index Fund Institutional Shares—Fund Number 838

Vanguard funds are not sponsored, endorsed, sold, or promoted by the University of Chicago or its Center for Research in Security Prices, and neither the University of Chicago nor its Center for Research in Security Prices makes any representation regarding the advisability of investing in the funds.

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).

SPI 838 122019