The investment seeks to track the investment results of an index composed of underlying fixed income funds that collectively seek to deliver current income. The fund invests primarily in underlying funds that themselves seek investment results corresponding to their own underlying indexes. The fund also invests in a combination of other exchange-traded funds ("ETFs") (including other iShares ETFs), cash and cash equivalents, including shares of money market funds advised by BFA or its affiliates ("BlackRock Cash Funds"). The underlying index is a broadly diversified fixed income index that seeks to deliver current income.