All U.S. jurisdictions recognize common-law marriages that were validly contracted in the originating jurisdiction, because they are valid marriages in the jurisdiction where they were contracted (see Full Faith and Credit Clause). However, absent legal registration or similar notice of the marriage, the parties to a common law marriage or their eventual heirs may have difficulty proving their relationship to be marriage. Some states provide for registration of an informal or common-law marriage based on the declaration of each of the spouses on a state-issued form.