This document contains final regulations relating to sales or exchanges of interests in partnerships, S corporations, and trusts. The regulations interpret the look-through provisions of section 1(h), added by section 311 of the Taxpayer Relief Act of 1997 and amended by sections 5001 and 6005(d) of the Internal Revenue Service Restructuring and Reform Act of 1998, and explain the rules relating to the division of the holding period of a partnership interest. The regulations affect partnerships, partners, S corporations, S corporation shareholders, trusts, and trust beneficiaries.