This document contains final regulations that provide additional guidance regarding the limitation on the deduction for business interest expense under section 163(j) of the Internal Revenue Code (Code) to reflect amendments made by the Tax Cuts and Jobs Act and the Coronavirus Aid, Relief, and Economic Security Act. Specifically, the regulations address the application of the limitation in contexts involving passthrough entities, regulated investment companies (RICs), and controlled foreign corporations. The regulations also provide guidance regarding the definitions of real property development, real property redevelopment, and syndicate. The regulations affect taxpayers that have business interest expense, particularly passthrough entities, their partners and shareholders, as well as foreign corporations and their United States shareholders. The regulations also affect RICs that have business interest income, RIC shareholders that have business interest expense, and corporations that are members of a consolidated group.