The Fund seeks to track the investment results of the Russell 1000® Pure Domestic Exposure Index (the “Underlying Index”), which is designed to reflect the performance of the common stock of companies that earn a higher percentage of their revenues through sales in the U.S. as compared to other large- and mid-capitalization companies in the U.S. equity market. The Underlying Index is a subset of the market capitalization-weighted Russell 1000 Index. All companies in the Russell 1000 Index that have a domestic sales ratio of 90% or greater will be included in the Underlying Index. Domestic sales ratio is calculated as the percentage of a company’s latest reported domestic revenues compared to the company's total revenues as of the data cut-off date. The Underlying Index will be reviewed and reconstituted annually in September using data at the close of the last business day of August (the data cut-off date). As of March 31, 2021, a significant portion of the Underlying Index is represented by securities of companies in the consumer discretionary and financials industries or sectors. The components of the Underlying Index are likely to change over time. The companies included in the Underlying Index may change over time, including changes based on a company's domestic sales ratio for inclusion in the Underlying Index. In addition, the weighting of a particular company in the Underlying Index may change over time depending on its market capitalization relative to other companies included 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 capitalization and industry weightings), fundamental characteristics (such as return variability 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 80% of its assets in the component securities of its Underlying Index and in investments that have economic characteristics that are substantially identical to the component securities of its Underlying Index (i.e., depositary receipts representing 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 money market funds advised by BFA or its affiliates, as well as in securities not included in the Underlying Index, but which BFA believes will help the Fund track the Underlying Index. Cash and cash equivalent investments associated with a derivative position will be treated as part of that position for the purposes of calculating investments not included in the Underlying Index. The Fund seeks to track the investment results of the Underlying Index before fees and expenses of the Fund. 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 FTSE Russell (the “Index Provider” or “Russell”), which is part of the London Stock Exchange Group and 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) and repurchase agreements collateralized by U.S. government securities are not considered to be issued by members of any industry.