The Invesco National AMT-Free Municipal Bond ETF (PZA) aims to track the investment results of The ICE BofAML National Long-Term Core Plus Municipal Securities Index. The ETF typically allocates a minimum of 80% of its total holdings to municipal bonds that are both constituents of this Index and exempt from the federal alternative minimum tax. The underlying Index is composed of U.S. dollar-denominated, high-quality, tax-exempt debt instruments publicly issued by U.S. states, territories, or their local government entities within the domestic market, provided they have a remaining maturity of at least 15 years. The Index components are adjusted monthly and weighted by their current outstanding market value. Instead of purchasing every security in the Index, the Fund employs a "sampling" methodology, investing in a representative selection of bonds to fulfill its investment objective. Both the Fund and its benchmark Index undergo monthly rebalancing and reconstitution.