A marriage license is required by every state to legalize a marriage. The marriage license must be obtained in the county the marriage occurs, even if the spouses reside elsewhere. The marriage license must be signed by the spouses and the officiant. Some states also require witness signatures. A marriage license must be filed with the state in order to be valid. Marriage licenses are used to prove new legal obligations, such as Social Security, insurance, medical, and survivor benefits. They also guard against illegal unions between underage individuals or familial or bigamous unions.