The Fund seeks to track the investment results of the S&P AMT-Free Municipal Series Dec 2021 IndexTM (the “Underlying Index”), which measures the performance of investment-grade (as determined by S&P Dow Jones Indices LLC (the “Index Provider” or “SPDJI”)), tax-exempt U.S. municipal bonds maturing in 2021. As of October 31, 2020, there were 14,820 issues in the Underlying Index. The Underlying Index includes municipal bonds primarily from issuers that are state or local governments or agencies such that the interest on the bonds is exempt from U.S. federal income taxes and the federal alternative minimum tax (“AMT”). Each bond must have a rating of at least BBB- by S&P Global Ratings, Baa3 by Moody’s Investors Service, Inc. (“Moody's”), or BBB- by Fitch Ratings, Inc. and must have a minimum maturity par amount of $2 million to be eligible for inclusion in the Underlying Index. To remain in the Underlying Index, bonds must maintain a minimum par amount greater than or equal to $2 million as of each rebalancing date. All bonds in the Underlying Index will mature after December 31, 2020 and before December 2, 2021. Bonds in the Underlying Index that mature or are pre-refunded in their respective year of maturity do not accrue interest past the maturity or pre-refund date. The Fund is a series of the iShares iBonds® fixed maturity series of bond exchange-traded funds (“ETFs”) sponsored by BlackRock, Inc. (“BlackRock”). The iBonds® fixed maturity series do not invest in U.S. savings bonds or other U.S. government bonds (except to the extent the funds hold cash equivalent instruments consistent with their investment objectives) and are not designed to provide protection against inflation. 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 will generally hold municipal bond securities issued by state and local municipalities whose interest payments are exempt from U.S. federal income tax, the federal AMT and the federal Medicare contribution tax of 3.8% on “net investment income,” including dividends, interest and capital gains. In the last months of operation, as the bonds held by the Fund mature, the proceeds will not be reinvested in bonds but instead will be held in cash and cash equivalents, including, without limitation, shares of BlackRock Cash Funds, AMT-free tax-exempt municipal notes, variable rate demand notes and obligations, tender option bonds and municipal commercial paper. These cash equivalents may not be included in the Underlying Index. By December 2, 2021, the Underlying Index is expected to consist entirely of cash earned in this manner. Around the same time, the Fund will wind up and terminate, and its net assets will be distributed to then-current shareholders. The Fund seeks to track the investment results of the Underlying Index before fees and expenses of the Fund. The Underlying Index is sponsored by SPDJI, 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. Industry Concentration Policy. The Fund will concentrate its investments (i.e., hold 25% or more of its total assets) in a particular industry or group of industries to approximately the same extent that the Underlying Index is concentrated. For purposes of this limitation, securities of the U.S. government (including its agencies and instrumentalities), repurchase agreements collateralized by U.S. government securities, and securities of state or municipal governments andtheir political subdivisions are not considered to be issued by members of any industry.