Unlike U.S. taxpayers ??? who are subject to U.S. federal income tax on their worldwide income ??? non-U.S. taxpayers generally are subject to U.S. taxation on two categories of income: 1) certain passive types of U.S.-source income, e.g., interest, dividends, rents, annuities, and other types of income known as FDAP;5 and 2) income that is effectively connected to a U.S. trade or business (ECI).6