Strategy. The Fund seeks to track the investment results of the Russell 2500 TM Index (the Underlying Index ), which measures the performance of the small- to mid-capitalization sector of the U.S. equity market, as defined by FTSE Russell (the Index Provider or Russell ). The Underlying Index is a subset of the Russell 3000 Index, which measures the performance of the broad U.S. equity market, as defined by Russell. The Underlying Index is a float-adjusted capitalization-weighted index of equity securities issued by approximately 2,500 of the smallest issuers in the Russell 3000 Index. As of March 31, 2025, the Underlying Index represented approximately 12% of the total market capitalization of the Russell 3000 Index. As of March 31, 2025, a … Show more… The Fund seeks to track the investment results of the Russell 2500 TM Index (the Underlying Index ), which measures the performance of the small- to mid-capitalization sector of the U.S. equity market, as defined by FTSE Russell (the Index Provider or Russell ). The Underlying Index is a subset of the Russell 3000 Index, which measures the performance of the broad U.S. equity market, as defined by Russell. The Underlying Index is a float-adjusted capitalization-weighted index of equity securities issued by approximately 2,500 of the smallest issuers in the Russell 3000 Index. As of March 31, 2025, the Underlying Index represented approximately 12% of the total market capitalization of the Russell 3000 Index. As of March 31, 2025, a significant portion of the Underlying Index is represented by securities of companies in the financial and industrials industries or sectors. The components of the Underlying Index are likely to change over time. Currently, the Fund seeks to achieve its investment objective by investing a substantial portion of its assets in the Underlying Fund. However, BFA is not required to invest any portion, or any particular percentage, of the Fund's assets in the Underlying Fund. BFA uses an indexing approach to try to achieve the Funds investment objective. 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 and the Underlying 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 applicable Underlying Index. The Fund generally will invest at least 80% of its assets in the component securities of its 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 the percentage of investments 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 Russell, which is part of the London Stock Exchange Group and is independent of the Fund and BFA. Russell 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. Show less