What is the difference between civil partnership and a marriage?

A civil union is a legal mechanism, sanctioned by civil authority, intended to grant same-gender couples legal status somewhat similar to civil marriage. In states with civil unions, same-gender couples are granted the same state-level rights, benefits, and protections as those granted to heterosexual married couples. No other states recognize civil unions. As such, same-gender couples considered to be legally united in states with unions are treated as single individuals when they cross into other states.

Unlike the national governments of some foreign countries, the US federal government does not recognize civil unions. As a result, >1000 federal rights, benefits, and protections are not made available to same-gender couples joined by civil union in the United States.

A domestic partnership is a relationship between 2 individuals, often but not necessarily of the same gender, who live together and mutually support one another as spouses but who are not legally joined in a civil marriage or a civil union. Some same-gender couples enter into domestic partnership agreements to create legally enforceable contracts involving property, finances, inheritance, and/or health care. Domestic partnership do not reach the same legal threshold as civil unions or civil marriages and, accordingly, do not afford couples the rights, benefits, and protections of civil marriage.