This document contains final regulations under section 645 relating to an election for certain revocable trusts to be treated and taxed as part of an estate. The final regulations provide the procedures and requirements for making the election, rules regarding the tax treatment of the trust and the estate while the election is in effect, and rules regarding the termination of the election. This document also contains final regulations clarifying the reporting rules for a trust, or portion of a trust, that is treated as owned by the grantor, or another person under the provisions of subpart E, part I, subchapter J, chapter 1 of the Internal Revenue Code, for the taxable year ending with the death of the grantor or other person.