This document contains final regulations concerning separate share rules applicable to estates under section 663(c) of the Internal Revenue Code. These regulations provide that substantively separate and independent shares of different beneficiaries are to be treated as separate estates for purposes of computing distributable net income and applying the distribution provisions of sections 661 and 662. These regulations also provide that a surviving spouse's statutory elective share of a decedent's estate and a pecuniary formula bequest are separate shares. Further, a revocable trust that elects to be treated as part of a decedent's estate is a separate share.