Vanguard Institutional Index Fund (VIIIX) N-CSRSCertified semi-annual shareholder report (management investment company)

3.  Swap Contracts: The fund has entered into equity swap contracts to earn the total return on selected reference stocks in the fund’s target index. Under the terms of the swaps, the fund receives the total return on the referenced stock (i.e., receiving the increase or paying the decrease in value of the selected reference stock and receiving the equivalent of any dividends in respect of the selected referenced stock) over a specified period of time, applied to a notional amount that represents the value of a designated number of shares of the selected reference stock at the beginning of the equity swap contract. The fund also pays a floating rate that is based on short-term interest rates, applied to the notional amount. At the same time, the fund generally invests an amount approximating the notional amount of the swap in high-quality temporary cash investments.

A risk associated with all types of swaps is the possibility that a counterparty may default on its obligation to pay net amounts due to the fund. The fund’s maximum amount subject to counterparty risk is the unrealized appreciation on the swap contract. The fund mitigates its counterparty risk by entering into swaps only with a diverse group of prequalified counterparties, monitoring their financial strength, entering into master netting arrangements with its counterparties, and requiring its counterparties to transfer collateral as security for their performance. In the absence of a default, the collateral pledged or received by the fund cannot be repledged, resold, or rehypothecated. In the event of a counterparty’s default (including bankruptcy), the fund may terminate any swap contracts with that counterparty, determine the net amount owed by either party in accordance with its master netting arrangements, and sell or retain any collateral held up to the net amount owed to the fund under the master netting arrangements. The swap contracts contain provisions whereby a counterparty may terminate open contracts if the fund’s net assets decline below a certain level, triggering a payment by the fund if the fund is in a net liability position at the time of the termination. The payment amount would be reduced by any collateral the fund has pledged. Any securities pledged as collateral for open contracts are noted in the Schedule of Investments. The value of collateral received or pledged is compared daily to the value of the swap contracts exposure with each counterparty, and any difference, if in excess of a specified minimum transfer amount, is adjusted and settled within two business days.

The notional amounts of swap contracts are not recorded in the Statement of Assets and Liabilities. Swaps are valued daily based on market quotations received from independent pricing services or recognized dealers and the change in value is recorded in the Statement of Assets and Liabilities as an asset (liability) and in the Statement of Operations as unrealized appreciation (depreciation) until periodic payments are made or the termination of the swap, at which time realized gain (loss) is recorded.

During the six months ended June 30, 2021, the fund’s average amounts of investments in total return swaps represented less than 1% of net assets, based on the average of notional amounts at each quarter-end during the period.

4. Federal Income Taxes: The fund intends to continue to qualify as a regulated investment company and distribute all of its taxable income. The fund’s tax returns are open to examination by the relevant tax authorities until expiration of the applicable statute of limitations, which is generally three years after the filing of the tax return. Management has analyzed the fund’s tax positions taken for all open federal and state income tax years, and has concluded that no provision for income tax is required in the fund’s financial statements.

5. Distributions: Distributions to shareholders are recorded on the ex-dividend date. Distributions are determined on a tax basis at the fiscal year-end and may differ from net investment income and realized capital gains for financial reporting purposes.

6. Securities Lending: To earn additional income, the fund lends its securities to qualified institutional borrowers. Security loans are subject to termination by the fund at any time, and are required to be secured at all times by collateral in an amount at least equal to the market value of securities loaned. Daily market fluctuations could cause the value of loaned securities to be more or less than the value of the collateral received. When this occurs, the collateral is adjusted and settled before the opening of the market on the next business day. The fund further mitigates its counterparty risk by entering into securities lending transactions only with a diverse group of prequalified counterparties, monitoring their financial strength, and entering into master securities lending agreements with its counterparties. The master securities lending agreements provide that, in the event of a counterparty’s default (including bankruptcy), the fund may terminate any loans with that borrower, determine the net amount owed, and sell or retain the collateral up to the net amount owed to the fund; however, such actions may be subject to legal proceedings. While collateral mitigates counterparty risk, in the event of a default, the fund may experience delays and costs in recovering the securities loaned. The fund invests cash collateral received in Vanguard Market Liquidity Fund, and records a liability in the Statement of Assets and Liabilities for the return of the collateral, during the period the securities are on loan. Collateral investments in Vanguard Market Liquidity Fund are subject to market appreciation or depreciation. Securities lending income represents fees charged to borrowers plus income earned on invested cash collateral, less expenses associated with the loan. During the term of the loan, the fund is entitled to all distributions made on or in respect of the loaned securities.

7. Credit Facilities and Interfund Lending Program: The fund and certain other funds managed by The Vanguard Group ("Vanguard") participate in a $4.3 billion committed credit facility provided by a syndicate of lenders pursuant to a credit agreement and an uncommitted credit facility provided by Vanguard. Both facilities may be renewed annually. Each fund is individually liable for its borrowings, if any, under the credit facilities. Borrowings may be utilized for temporary or emergency purposes, subject to the fund’s regulatory and contractual borrowing restrictions. With respect to the committed credit facility, the participating funds are charged administrative fees and an annual commitment fee of 0.10% of the undrawn committed amount of the facility; these fees are allocated to the funds based on a method approved by the fund’s board of trustees and included in Management and Administrative expenses on the fund’s Statement of Operations. Any borrowings under either facility bear interest at a rate based upon the higher of the one-month London Interbank Offered Rate (or an acceptable alternate rate, if necessary), federal funds effective rate, or overnight bank funding rate plus an agreed-upon spread, except that borrowings under the uncommitted credit facility may bear interest based upon an alternate rate agreed to by the fund and Vanguard.

In accordance with an exemptive order (the “Order”) from the SEC, the fund may participate in a joint lending and borrowing program that allows registered open-end Vanguard funds to borrow money from and lend money to each other for temporary or emergency purposes (the “Interfund Lending Program”), subject to compliance with the terms and conditions of the Order, and to the extent permitted by the fund’s investment objective and investment policies. Interfund loans and borrowings normally extend overnight, but can have a maximum duration of seven days. Loans may be called on one business day’s notice. The interest rate to be charged is governed by the conditions of the Order and internal procedures adopted by the board of trustees. The board of trustees is responsible for overseeing the Interfund Lending Program.

For the six months ended June 30, 2021, the fund did not utilize the credit facilities or the Interfund Lending Program.

8. Other: Dividend income is recorded on the ex-dividend date. Non-cash dividends included in income, if any, are recorded at the fair value of the securities received. Interest income includes income distributions received from Vanguard Market Liquidity Fund and is accrued daily. Premiums and discounts on debt securities are amortized and accreted, respectively, to interest income over the lives of the respective securities, except for premiums on certain callable debt securities that are amortized to the earliest call date. Security transactions are accounted for on the date securities are bought or sold. Costs used to determine realized gains (losses) on the sale of investment securities are those of the specific securities sold.

Each class of shares has equal rights as to assets and earnings, except that each class separately bears certain class-specific expenses related to maintenance of shareholder accounts (included in Management and Administrative expenses) and shareholder reporting. Marketing and distribution expenses are allocated to each class of shares based on a method approved by the board of trustees. Income, other non-class-specific expenses, and gains and losses on investments are allocated to each class of shares based on its relative net assets.

Upon the request of Vanguard, the fund may invest up to 0.40% of its net assets as capital in Vanguard. At June 30, 2021, the fund had contributed to Vanguard capital in the amount of $9,824,000, representing less than 0.01% of the fund’s net assets and 3.93% of Vanguard’s capital received pursuant to the FSA. The fund’s trustees and officers are also directors and employees, respectively, of Vanguard.

The following table summarizes the market value of the fund’s investments and derivatives as of June 30, 2021, based on the inputs used to value them:

The fund purchased securities from and sold securities to other Vanguard funds or accounts managed by Vanguard or its affiliates, in accordance with procedures adopted by the board of trustees in compliance with Rule 17a-7 of the Investment Company Act of 1940. For the six months ended ended June 30, 2021, such purchases and sales were $675,391,000 and $332,854,000, respectively; these amounts, other than temporary cash investments, are included in the purchases and sales of investment securities noted above.