What is common law marriage?

The three requirements

1. Capacity and cohabitation. Both partners must be legally able to marry and must live together. There is no magic number of years — the «seven years» rule is a myth.
2. Present agreement to be married. Not a plan to marry later; an agreement that you are married now.
3. Holding out. Acting publicly as spouses: using the same surname, filing joint tax returns, naming each other as spouse on insurance or benefit forms, introducing each other as husband or wife.

What it means once it exists

Everything a licensed marriage means: property rights, spousal inheritance, the ability to make medical decisions, eligibility for spousal benefits, and the requirement of a formal divorce to dissolve it. There is no such thing as a common law divorce.

Recognition across state lines

A common law marriage validly created in a state that allows it is generally recognised in every other state, under the full-faith-and-credit principle and the traditional place-of-celebration rule. So a couple married this way in Colorado remains married after moving to California, which does not create such marriages itself.

How disputes usually arise

Almost always after a death or a separation, when one partner claims the marriage and the other denies it. Proof is documentary: joint tax filings, deeds, beneficiary designations, affidavits from friends and family. The burden falls on the person asserting the marriage, and vague testimony rarely carries it.