Civil unions between same-sex couples were legalised in Denmark, the first country to do so.

A civil union is a legally recognized arrangement similar to marriage, primarily created to provide legal recognition for same-sex couples. Civil unions grant some or all of the rights of marriage, with child adoption being a common exception.

A same-sex relationship is a romantic or sexual relationship between people of the same sex. Same-sex marriage refers to the institutionalized recognition of such relationships in the form of a marriage; civil unions exist in some countries where same-sex marriage does not.

Same-sex marriage has been legal in Denmark since 15 June 2012. A bill for the legalization of same-sex marriages was introduced by the Thorning-Schmidt I Cabinet, and approved 85–24 by the Folketing on 7 June 2012. It received royal assent by Queen Margrethe II on 12 June and took effect three days later. Polling indicates that a significant majority of Danes support the legal recognition of same-sex marriage. Denmark was the fourth Nordic country, after Norway, Sweden and Iceland, the eighth in Europe and the eleventh in the world to legalize same-sex marriage. It was the first country in the world to enact registered partnerships, which provided same-sex couples with almost all of the rights and benefits of marriage, in 1989.