A "common law marriage" is a union that hasn't been licensed by the state but that some states nevertheless accept as a legal marriage. Although you don't need an official piece of paper from the state to enter into a common law marriage, you can't get out of one without an official piece of paper from the state---because once you're married, you have to get a divorce just like everyone else.
Significance
Any couple can declare themselves "married" by common law, but only a handful of states consider such marriages to have legal weight. As of 2010, according to the National Conference of State Legislatures, the District of Columbia and eight states recognized common law marriages: Alabama, Colorado, Kansas, Rhode Island, South Carolina, Iowa, Montana, Oklahoma and Texas. Five other states recognized common law marriages only if they were established before a certain date: Georgia, with a cutoff date of Jan. 1, 1997; Idaho, Jan. 1, 1996; Ohio, Oct. 10, 1991; Oklahoma, Nov. 1, 1998; and Pennsylvania, Jan. 1, 2005. If you haven't lived in one of these states, you don't need a divorce to end a common-law marriage, because as far as the state is concerned, you were never married.
Identification
States that recognize marriages in common law have varying definitions of when a couple qualifies as married, and you should check the applicable statues in your state. However, there's generally a three-part test: Do you agree that you are married? Do you live together and maintain a household? Do you present yourself to the world as husband and wife? If the answer to all three is yes, then your relationship may qualify as a common-law marriage. To get out of it, you need to file for divorce. Contrary to what some people believe, simply living together, no matter how long, is not enough to establish a common-law marriage.
Divorce
The requirements for obtaining a legal divorce are the same for common-law marriages as marriages licensed by the state. Check with your state law for the particulars. As the National Conference on State Legislatures says, "There is no such thing as common law divorce," the way there is common law marriage. You can only get a divorce by court order.
Principle
States that recognize common law marriages require formal divorce based on the legal principle of "estoppel": You can't claim one thing one day, then deny it the next when it's no longer convenient. If you want to claim all the societal benefits that accompany marriage, then you have to accept the societal responsibilities, too.
Consideration
What if you've left the state where you established your common law marriage? Do you need a divorce then? Under the Constitution, states are required to recognize the "public acts" and "judicial proceedings" conducted in other states. This usually applies to marriages, but common law marriage is, by definition, neither a public---that is, government---act nor a judicial proceeding. So the legal status of common law issues across state borders remains "murky," in the words of the Alternatives to Marriage Project.
