Strategy. The Fund seeks to track the investment results of the MSCI USA Mid Cap Diversified Multiple-Factor Index (the Underlying Index), which has been developed by MSCI Inc. (the Index Provider or MSCI). Mid-capitalization companies, as defined by the Index Provider, represent the companies between approximately 70%-85% of the available free float-adjusted market capitalization for the U.S. The Underlying Index is designed to select equity securities from the MSCI USA Mid Cap Index (the Parent Index) that have high exposure to four investment style factors value, quality, momentum and low size while maintaining a level of risk similar to that of the Parent Index. The Underlying Index is also constrained in its construction to limit turnover and extreme exposures to particular … Show more… The Fund seeks to track the investment results of the MSCI USA Mid Cap Diversified Multiple-Factor Index (the Underlying Index), which has been developed by MSCI Inc. (the Index Provider or MSCI). Mid-capitalization companies, as defined by the Index Provider, represent the companies between approximately 70%-85% of the available free float-adjusted market capitalization for the U.S. The Underlying Index is designed to select equity securities from the MSCI USA Mid Cap Index (the Parent Index) that have high exposure to four investment style factors value, quality, momentum and low size while maintaining a level of risk similar to that of the Parent Index. The Underlying Index is also constrained in its construction to limit turnover and extreme exposures to particular sectors, component weights or other investment style factors relative to the Parent Index. For example, on each rebalance date, the sector weights of the Underlying Index will not deviate more than +/-5% from the sector weights of the Parent Index. MSCI, in selecting equity securities from the Parent Index, assigns a composite score for a security through a proprietary model based on four equally-weighted investment style factors. The value score is calculated from a companys valuation ratios, such as forward and trailing earnings to share price, cash earnings to share price, book value to share price and enterprise value to earnings before interest and taxes. The quality score is calculated from a companys underlying metrics, including profitability metrics (asset turnover, gross profitability, gross margin and return on assets), investment quality metrics (total assets growth rate, issuance growth and capital expenditure growth), leverage ratios (market leverage, book leverage and debt-to-assets ratio) and earnings variability (measured by volatility of earnings, cash flow, sales, and forward earnings estimates to share price). The momentum score aims to measure a security's sustained relative performance against the global market over a two-year period and against other securities based in the same country over the previous 12 months (with a one-month lag). The low size score seeks to measure the market capitalization of a company as compared to other companies based in the same country. The Underlying Index consisted of securities from approximately 729 companies from 40 countries or regions as of May 17, 2022. As of May 17, 2022, a significant portion of the Underlying Index is represented by securities of companies in the information technology industry or sector. The components of the Underlying Index are likely to change over time. The Underlying Index is rebalanced on a quarterly basis, usually as of the close of the last business day of February, May, August and November, coinciding with the regular Index Reviews (Semi-Annual Index Reviews in May and November and Quarterly Index Reviews in February and August) of the MSCI Global Investable Market Indexes. BFA uses a passive or indexing approach to try to achieve the Funds 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 and Parent Index are sponsored by MSCI, 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 Parent Index and publishes information regarding the market value of the Underlying Index and Parent 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