The investment seeks to track the investment results of an index composed of the principal payments of U.S. Treasury bonds (specifically principal ?STRIPS?, also known as ?Separate Trading of Registered Interest and Principal of Securities?) with remaining maturities of at least 25 years. The fund seeks to track the investment results of the ICE BofA Long US Treasury Principal STRIPS Index, which measures the performance of long maturity Separate Trading of Registered Interest and Principal of Securities (?STRIPS?) representing the final principal payment of U.S. Treasury bonds. BFA uses a representative sampling indexing strategy to manage the fund.