The Fund seeks to meet its investment objective generally by investing in individual securities which satisfy the criteria of the ICE 2021 Maturity US Treasury Index (the “Underlying Index”). The Fund may also invest in short-term paper, cash and cash equivalents, including shares of money market funds advised by BFA or its affiliates. The Fund is a term fund that will terminate on or about December 15, 2021, at which time it will distribute its remaining net assets to shareholders pursuant to a plan of liquidation. The Fund does not seek to return any predetermined amount at maturity or in periodic distributions. The Underlying Index consists of publicly-issued U.S. Treasury securities that are scheduled to mature after December 31, 2020 and before December 16, 2021. Qualifying securities are U.S. Treasury notes and bonds having $1 billion or more of outstanding face value, excluding amounts held by the Federal Reserve System Open Market Account (“SOMA”). In addition, the securities in the Underlying Index must have a fixed coupon schedule and be denominated in U.S. dollars. Excluded from the Underlying Index are inflation-linked securities, Treasury bills, cash management bills, any government agency debt issued with or without a government guarantee and zero-coupon issues that have been stripped from coupon-paying bonds. However, the amounts outstanding of qualifying securities in the Underlying Index are not reduced by any individual components of such securities (i.e., coupon or principal) that have been stripped after inclusion in the Underlying Index. The Underlying Index is market value weighted based on amounts outstanding reduced by amounts held by the Federal Reserve SOMA. Accrued interest is calculated assuming next-day settlement. The Underlying Index is rebalanced on the last calendar day of the month, based on information available up to and including the third business day before the last business day of the month. New issues must settle on or before the calendar month end rebalancing date in order to qualify for the upcoming month. The securities in the Underlying Index are updated on the last calendar day of each month until six months prior to maturity. Cash flows from bond payments that are received during the month are retained in the Underlying Index until the end of the month and then are removed as part of the rebalancing. Beginning June 30, 2021, the Underlying Index will not remove interest payments and matured securities at each rebalancing but instead will retain those amounts as a growing cash position throughout the remaining life of the Underlying Index. As the Fund approaches its termination date, its holdings of money market funds or similar funds may increase, causing the Fund to incur fees and expenses of such funds. By December 15, 2021, the Underlying Index value will be represented almost entirely by cash as no securities will remain in the Underlying Index. BFA uses a “passive” or indexing approach to try to achieve the Fund’s investment objective. Unlike many investment companies, the Fund does not try to “beat” the index it tracks and does not seek temporary defensive positions when markets decline or appear overvalued. Indexing may eliminate the chance that the Fund will substantially outperform the Underlying Index but also may reduce some of the risks of active management, such as poor security selection. Indexing seeks to achieve lower costs and better after-tax performance by aiming to keep portfolio turnover low in comparison to actively managed investment companies. BFA uses a representative sampling indexing strategy to manage the Fund. “Representative sampling” is an indexing strategy that involves investing in a representative sample of securities that collectively has an investment profile similar to that of an applicable underlying index. The securities selected are expected to have, in the aggregate, investment characteristics (based on factors such as market value and industry weightings), fundamental characteristics (such as return variability, duration, maturity, credit ratings and yield) and liquidity measures similar to those of an applicable underlying index. The Fund may or may not hold all of the securities in the Underlying Index. The Fund generally will invest at least 90% of its assets in the component securities of the Underlying Index, except during the last months of the Fund’s operations, as described below, and may invest up to 10% of its assets in certain futures, options and swap contracts, cash and cash equivalents, including shares of money market funds advised by BFA or its affiliates (“BlackRock Cash Funds”), as well as in securities not included in the Underlying Index, but which BFA believes will help the Fund track the Underlying Index. From time to time when conditions warrant, however, the Fund may invest at least 80% of its assets in the component securities of the Underlying Index and may invest up to 20% of its assets in certain futures, options and swap contracts, cash and cash equivalents, including shares of BlackRock Cash Funds, as well as in securities not included in the Underlying Index, but which BFA believes will help the Fund track the Underlying Index. The Fund seeks to track the investment results of the Underlying Index before fees and expenses of the Fund. In the last months of operation, as the bonds held by the Fund mature, the proceeds will not be reinvested by the Fund in bonds but instead will be held in cash and cash equivalents. By December 15, 2021, the Underlying Index is expected to consist almost entirely of cash earned in this manner. On or around this date, the Fund will wind up and terminate, and its net assets will be distributed to then-current shareholders pursuant to a plan of liquidation. The Fund may lend securities representing up to one-third of the value of the Fund's total assets (including the value of any collateral received). The Underlying Index is sponsored by ICE Data Indices, LLC or its affiliates (collectively, the “Index Provider” or “IDI”), which is independent of the Fund and BFA. The Index Provider determines the composition and relative weightings of the securities in the Underlying Index and publishes information regarding the market value of the Underlying Index.