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Vanguard Extended Duration Treasury Index Fund

Summary Prospectus

December 23, 2014

Institutional Shares & Institutional Plus Shares

Vanguard Extended Duration Treasury Index Fund Institutional Shares (VEDTX)

Vanguard Extended Duration Treasury Index Fund Institutional Plus Shares (VEDIX)

The Fund’s statutory Prospectus and Statement of Additional Information dated December 23, 2014, 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 e-mail request to online@vanguard.com.

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.

Investment Objective

The Fund seeks to track the performance of an index of extended-duration zero-coupon U.S. Treasury securities.

Fees and Expenses

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


Shareholder Fees
(Fees paid directly from your investment)
	Institutional	Institutional Plus
	Shares	Shares
Sales Charge (Load) Imposed on Purchases	None	None
Purchase Fee (other than on reinvested dividends or capital gains)	0.50%	0.50%
Sales Charge (Load) Imposed on Reinvested Dividends	None	None
Redemption Fee	None	None

Annual Fund Operating Expenses
(Expenses that you pay each year as a percentage of the value of your investment)
	Institutional	Institutional Plus
	Shares	Shares
Management Fees	0.07%	0.06%
12b-1 Distribution Fee	None	None
Other Expenses	0.03%	0.02%
Total Annual Fund Operating Expenses	0.10%	0.08%

Examples

The following examples are intended to help you compare the cost of investing in the Fund’s Institutional Shares or Institutional Plus Shares with the cost of investing in other mutual funds. They illustrate the hypothetical expenses that you would incur over various periods if you invested $10,000 in the Fund’s shares. These examples assume that the Shares provide a return of 5% a year and that total annual fund operating expenses remain as stated in the preceding table. The results apply 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 Year	3 Years	5 Years	10 Years
Institutional Shares	$60	$82	$106	$178
Institutional Plus Shares	$58	$76	$95	$152

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 examples, reduce the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 17% of the average value of its portfolio.

Principal Investment Strategies

The Fund employs an indexing investment approach designed to track the performance of the Barclays U.S. Treasury STRIPS 20–30 Year Equal Par Bond Index. This Index includes zero-coupon U.S. Treasury securities (Treasury STRIPS), which are backed by the full faith and credit of the U.S. government, with maturities ranging from 20 to 30 years. A Treasury STRIP represents a single coupon payment, or a single principal payment, from a U.S. Treasury security that has been “stripped” into separately tradable components.

The Fund invests by sampling the Index, meaning that it holds a range of securities that, in the aggregate, approximates the full Index in terms of key risk factors, including duration, cash flow, and other characteristics. All of the Fund’s investments will be selected through the sampling process, and under normal circumstances, at least 80% of the Fund’s assets will be invested in U.S. Treasury securities held in the Index. The Fund maintains a dollar-weighted average maturity consistent with that of

the Index, which generally ranges between 20 and 30 years. The Fund is expected to have a duration that is greater than 20 years.

Principal Risks

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

• Interest rate risk, which is the chance that bond prices overall will decline because of rising interest rates. The prices of long-term bonds, such as those held by the Fund, are much more sensitive to interest rate changes than are the prices of short-term bonds. Interest rate risk is expected to be extremely high for the Fund because it invests primarily in zero-coupon long-term bonds, which have prices that are even more sensitive to interest rate changes than are coupon-bearing bonds of similar maturity. Because the Fund invests primarily in Treasury STRIPS with maturities ranging from 20 to 30 years, rising interest rates may cause the value of the Fund’s investments to decline significantly.

• Index sampling risk, which is the chance that the securities selected for the Fund, in the aggregate, will not provide investment performance matching that of the Fund’s target index. Index sampling risk for the Fund should be low.

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 (including annual fund operating expenses but excluding shareholder fees) has varied from one calendar year to another over the periods shown. If applicable shareholder fees were reflected, returns would be less than those shown in the bar chart. The table shows how the average annual total returns of the Institutional Shares (including annual fund operating expenses and any applicable shareholder fees) compare with those of the Fund‘s target index, which has investment characteristics similar to those of the Fund. The Fund’s Institutional Plus Shares have not been in operation long enough to report a full calendar-year return. Performance of the Fund’s Institutional Plus Shares would be substantially similar to that of the Institutional Shares because both share classes constitute an investment in the same portfolio of securities; their returns generally should differ only to the extent that the expenses of the two share classes differ. 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 Extended Duration Treasury Index Fund Institutional Shares¹

1 The year-to-date return as of the most recent calendar quarter, which ended on September 30, 2014, was 27.38%.

During the periods shown in the bar chart, the highest return for a calendar quarter was 52.05% (quarter ended September 30, 2011), and the lowest return for a quarter was –20.01% (quarter ended March 31, 2009).


Average Annual Total Returns for Periods Ended December 31, 2013

			Since
			Inception
			(Nov. 28,
	1 Year	5 Years	2007)
Vanguard Extended Duration Treasury Index Fund
Institutional Shares
Return Before Taxes	–21.28%	–2.42%	5.15%
Return After Taxes on Distributions	–22.67	–4.91	2.72
Return After Taxes on Distributions and Sale of Fund Shares	–11.79	–2.57	3.23
Barclays U.S. Treasury STRIPS 20-30 Year Equal Par
Bond Index
(reflects no deduction for fees, expenses, or taxes)	–20.54%	–1.81%	5.61%

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

William D. Baird, Portfolio Manager at Vanguard. He has co-managed the Fund since 2013.

Joshua C. Barrickman, CFA, Principal of Vanguard and head of Vanguard’s Fixed Income Indexing Americas. He has co-managed the Fund since 2013.

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 or Institutional Plus Shares is $5 million or $100 million, respectively. The minimum investment amount required to add to an existing Fund account is generally $1.

Tax Information

The Fund’s distributions may be taxable as ordinary income or capital gain. If you are investing through a tax-deferred retirement account, such as an IRA, 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 Extended Duration Treasury Index Fund Institutional Shares—Fund Number 1275

Vanguard Extended Duration Treasury Index Fund Institutional Plus Shares—Fund Number 1276

CFA^®is a registered trademark owned by CFA Institute.

Vanguard Extended Duration Treasury Index Fund is not sponsored, endorsed, issued, sold or promoted by Barclays Capital Inc. or any of its affiliates (“Barclays”). Barclays makes no representation or warranty, express or implied, to the owners or purchasers of Vanguard Extended Duration Treasury Index Fund or any member of the public regarding the advisability of investing in securities generally or in Vanguard Extended Duration Treasury Index Fund particularly or the ability of the Barclays Index to track general bond market performance. Barclays has not passed on the legality or suitability of the Vanguard Extended Duration Treasury Index Fund with respect to any person or entity. Barclays’ only relationship to Vanguard and Vanguard Extended Duration Treasury Index Fund is the licensing of the Barclays Index which is determined, composed and calculated by Barclays without regard to Vanguard or the Vanguard Extended Duration Treasury Index Fund or any owners or purchasers of the Vanguard Extended Duration Treasury Index Fund. Barclays has no obligation to take the needs of Vanguard, Vanguard Extended Duration Treasury Index Fund or the owners of Vanguard Extended Duration Treasury Index Fund into consideration in determining, composing or calculating the Barclays Index. Barclays is not responsible for and has not participated in the determination of the timing of, prices at, or quantities of Vanguard Extended Duration Treasury Index Fund to be issued. Barclays has no obligation or liability in connection with the administration, marketing or trading of the Vanguard Extended Duration Treasury Index Fund.

BARCLAYS SHALL HAVE NO LIABILITY TO THIRD PARTIES FOR THE QUALITY, ACCURACY AND/OR COMPLETENESS OF THE INDEX OR ANY DATA INCLUDED THEREIN OR FOR INTERRUPTIONS IN THE DELIVERY OF THE INDEX. BARCLAYS MAKES NO WARRANTY, EXPRESS OR IMPLIED, AS TO RESULTS TO BE OBTAINED BY OWNERS OF THE VANGUARD EXTENDED DURATION TREASURY INDEX FUND OR ANY OTHER PERSON OR ENTITY FROM THE USE OF THE INDEX OR ANY DATA INCLUDED THEREIN IN CONNECTION WITH THE RIGHTS LICENSED HEREUNDER OR FOR ANY OTHER USE. BARCLAYS RESERVES THE RIGHT TO CHANGE THE METHODS OF CALCULATION OR PUBLICATION, OR TO CEASE THE CALCULATION OR PUBLICATION OF THE BARCLAYS U.S. TREASURY STRIPS 20-30 YEAR EQUAL PAR BOND INDEX, AND BARCLAYS SHALL NOT BE LIABLE FOR ANY MISCALCULATION OF OR ANY INCORRECT, DELAYED OR INTERRUPTED PUBLICATION WITH RESPECT TO ANY OF THE BARCLAYS U.S. TREASURY STRIPS 20-30 YEAR EQUAL PAR BOND INDEX. BARCLAYS MAKES NO EXPRESS OR IMPLIED WARRANTIES, AND HEREBY EXPRESSLY DISCLAIMS ALL WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE OR USE WITH RESPECT TO THE INDEX OR ANY DATA INCLUDED THEREIN. BARCLAYS SHALL NOT BE LIABLE FOR ANY DAMAGES, INCLUDING, WITHOUT LIMITATION, ANY INDIRECT OR CONSEQUENTIAL DAMAGES RESULTING FROM THE USE OF THE INDEX OR ANY DATA INCLUDED THEREIN.

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