A civil union is a legally recognized arrangement similar to marriage, created primarily as a means to provide recognition in law for same-sex couples. Civil unions grant some or all of the rights of marriage.
Gay couple in Croatia, which allows civil partnerships but not same-sex marriage.
The notion of civil unions is rejected by some, such as this protester at a large demonstration in New York City against California Proposition 8.
Domestic partnership in California
A California domestic partnership is a legal relationship, analogous to marriage, created in 1999 to extend the rights and benefits of marriage to same-sex couples. It was extended to all opposite-sex couples as of January 1, 2016 and by January 1, 2020 to include new votes that updated SB-30 with more benefits and rights to California couples choosing domestic partnership before their wedding. California Governor Newsom signed into law on July 30, 2019.
Example of California domestic partnership certificate