Common law marriages are legally recognized in only nine states and the District of Columbia. Four other states have banned common law marriages but recognize common law marriages that existed before those bans. New Hampshire recognizes common law marriages solely for inheritance purposes. All states recognize common law marriages contracted in other states.
The requirements to contract a common law marriage vary by state, but include these common elements: cohabitation and presenting as a married couple. To present as a married, a couple might assume the same last name or file a joint tax return. Some states have further requirements, like Texas, which requires the registration of common law marriages with the county clerk, or Alabama, which requires the consummation of common law marriages.
Common law spouses occupy a precarious legal position. Laws around marital assets and family residences apply only to legally married couples, and in the case of the death of a common law spouse the surviving spouse may be excluded from inheritance. Furthermore, common law marriages are much harder to leave than they are to enter, and can only be dissolved by legal divorce.
The United States Supreme Court affirmed common law marriage in the 1877 case Meister v. Moore, where they ruled that states did not abolish common law marriage solely by establishing rules for regular marriages. In essence, common law marriage was legal anywhere it had not been specifically banned.