26 CFR § 31.7701-2
Definitions; spouse, husband and wife, husband, wife, marriage
June 25, 2020
(a) In general. For the definition of the terms spouse, husband and wife, husband, wife, and marriage, see §301.7701-18 of this chapter.
(b) Applicability date. The rules of this section apply to taxable years ending on or after September 2, 2016.
[T.D. 9785, 81 FR 60616, Sept. 2, 2016]