The Invesco National AMT-Free Municipal Bond ETF (Fund) is based on The ICE BofAML National Long-Term Core Plus Municipal Securities Index (Index). The Fund generally will invest at least 80% of its total assets in municipal securities that comprise the Index and that also are exempt from the federal alternative minimum tax. The Index is composed of US dollar-denominated, investment grade, tax-exempt debt publicly issued by US. states and territories, or their political subdivisions, in the US domestic market with a term of at least 15 years remaining to final maturity. The Index is adjusted monthly and its constituents are capitalization-weighted based on their current amount outstanding. The Fund does not purchase all of the securities in the Index; instead, the Fund utilizes a "sampling" methodology to seek to achieve its investment objective. The Fund and the Index are rebalanced and reconstituted monthly.