The most significant difference between marriage and civil unions (or domestic partnerships) is that only marriage offers federal benefits and protections.
Number of Legal Benefits:
Marriage: Over 1,049 federal and state level benefits
Civil Unions: Over 300 state level benefits. *No federal protection
Marriage: Couples can file both federal and state tax returns jointly.
Civil Unions: Couples can only file jointly in the state of civil registration.
Marriage: Partners can make emergency medical decisions.
Civil Unions: Partners can only make medical decisions in the registered state. Partners may not be able to make decisions out of state.
Marriage: Partners can transfer gifts to each other without tax penalty.
Civil Unions: Partners do not pay state taxes, but are required to report federal taxes.
Marriage: In the case of a partner's death, the spouse receives any earned Social Security or veteran benefits.
Civil Unions: Partners do not receive Social Security or any other government benefits in case of death.
Marriage: In case of divorce, individuals may have a legally-binding financial obligation to spouses and children.
Civil Unions: In the case of dissolution , no such spousal or child benefits are guaranteed or required out of state.
Marriage: U.S. citizens and legal residents can sponsor their spouses and family members for immigration.
Civil Unions: U.S. citizens and legal residents cannot sponsor non-legal spouses or family members.