Common law marriage—also known as marriage without formalities or informal marriage—is marriage without a wedding or marriage ceremony and without a marriage license. Some states recognize common law marriage under certain circumstances—such as when the parties agree to be married, live together (cohabit) after agreeing to be married, and represent to others that they are married (holding themselves out as a married couple).

Other states previously recognized common law marriages, but no longer recognize such marriages after a certain date on which the law was changed—usually by statute. In other states, common law marriage has not been recognized by the legislature in a statute, but the courts have recognized common law marriage in court opinions or case law.

In the state of Missouri, common law marriage is not recognized. Missouri law requires a license and a ceremony for a marriage to be considered valid. This means that no matter how long a couple has lived together or whether they hold themselves out as married, the state will not consider them legally married without the formalities of obtaining a marriage license and having a marriage ceremony. Couples who wish to have their relationship legally recognized as a marriage in Missouri must follow the traditional route of obtaining a marriage license and having a ceremony performed by an authorized individual. It's important for individuals in Missouri to be aware that cohabitation and intent to be considered married are not sufficient to establish a legal marriage under state law.