This document contains final regulations concerning the deduction for qualified business income under section 199A of the Internal Revenue Code (Code). The regulations will affect individuals, partnerships, S corporations, trusts, and estates engaged in domestic trades or businesses. The regulations also contain an anti-avoidance rule under section 643 of the Code to treat multiple trusts as a single trust in certain cases, which will affect trusts, their grantors, and beneficiaries. This document also requests additional comments on certain aspects of the deduction.