The fund normally invests at least 80% of its net assets in municipal bonds and debentures, the income from which is exempt from federal income tax (including the federal alternative minimum tax ("AMT")). It invests in a broadly diversified portfolio of federally tax-exempt municipal obligations issued by governmental authorities throughout the U.S. and its territories. The fund may invest in all types of municipal obligations, including pre-refunded bonds, general obligation bonds, revenue bonds, and municipal lease participations.