Idaho Code § 32-201: What constitutes marriage — No common-law marriage after January 1, 1996.

(1) Marriage is a personal relation arising out of a civil contract between a man and a woman, to which the consent of parties capable of making it is necessary. Consent alone will not constitute marriage; it must be followed by the issuance of a license and a solemnization as authorized and provided by law. Marriage created by a mutual assumption of marital rights, duties or obligations shall not be recognized as a lawful marriage.

(2) The provisions of subsection (1) of this section requiring the issuance of a license and a solemnization shall not invalidate any marriage contract in effect prior to January 1, 1996, created by consenting parties through a mutual assumption of marital rights, duties or obligations.