Civil partnerships in the United Kingdom, granted under the Civil Partnership Act 2004, allow same-sex couples to obtain essentially the same rights and responsibilities as civil marriage. Civil partners are entitled to the same property rights as married opposite-sex couples, the same exemption as married couples on inheritance tax, social security and pension benefits, and also the ability to get parental responsibility for a partner's children, as well as responsibility for reasonable maintenance of one's partner and their children, tenancy rights, full life insurance recognition, next of kin rights in hospitals, and others. There is a formal process for dissolving partnerships akin to divorce.

A civil union, also referred to by a variety of other names, is a legally recognized arrangement similar to marriage. These unions have been established in a number of countries since the late 1990s, often developing from less formal domestic partnership legislation. In Denmark, Iceland, Norway and Sweden, they have since been replaced, and in a number of other countries supplemented, by same-sex marriage. Civil unions are often seen by campaigners as a "first step" towards legalizing marriage for same-sex couples. While civil unions are predominantly established for both opposite-sex and same-sex couples, in a number of countries they are available to same-sex couples only.