Same-sex marriage
Same-sex marriage is marriage
Marriage is a social union or legal contract between people that creates kinship. It is an institution in which interpersonal relationships, usually intimate and sexual, are acknowledged in a variety of ways, depending on the culture or subculture in which it is found...

 between two persons of the same biological sex or social gender
Gender identity
A gender identity is the way in which an individual self-identifies with a gender category, for example, as being either a man or a woman, or in some cases being neither, which can be distinct from biological sex. Basic gender identity is usually formed by age three and is extremely difficult to...

. Supporters of legal recognition for same-sex marriage typically refer to such recognition as marriage equality.

Since 2001, ten countries have begun allowing same-sex couples to marry nationwide: Argentina, Belgium
Same-sex marriage in Belgium
On June 1, 2003, Belgium became the second country in the world to legally recognize same-sex marriage, with some restrictions. Originally, Belgium allowed the marriages of foreign same-sex couples only if their country of origin also allowed these unions...

, Canada
Same-sex marriage in Canada
On July 20, 2005, Canada became the fourth country in the world and the first country in the Americas to legalize same-sex marriage nationwide with the enactment of the Civil Marriage Act which provided a gender-neutral marriage definition...

, Iceland, the Netherlands
Same-sex marriage in the Netherlands
Same-sex marriage has been legal in the Netherlands since 1 April 2001...

, Norway
Same-sex marriage in Norway
Same-sex marriage became legal in Norway on January 1, 2009 when a gender neutral marriage bill was enacted after being passed by the Norwegian legislature in June 2008...

, Portugal
Same-sex marriage in Portugal
Same-sex marriage has been legal in Portugal since June 5, 2010. The government of Prime Minister José Sócrates introduced a bill for legalization in December 2009; it was passed by the Assembly of the Republic in February 2010. The bill was declared legally valid by the Portuguese Constitutional...

, Spain
Same-sex marriage in Spain
Same-sex marriage in Spain has been legal since July 3, 2005. In 2004, the nation's newly elected social democratic government, led by President José Luis Rodríguez Zapatero, began a campaign for its legalization, including the right of adoption by same-sex couples...

, South Africa
Same-sex marriage in South Africa
Same-sex marriage has been legal in South Africa since 30 November 2006, when the Civil Union Act, 2006 came into force, having been passed by Parliament earlier that month. A ruling by the Constitutional Court on 1 December 2005 had given Parliament one year to make same-sex marriage legal...

, and Sweden
Same-sex marriage in Sweden
Same-sex marriage in Sweden has been legal since 1 May 2009, following the adoption of a new, gender-neutral law on marriage by the Swedish parliament on 1 April 2009, making Sweden the seventh country in the world to open marriage to same sex couples nationwide...

. Same-sex marriages are also performed and recognized in Mexico City
Same-sex marriage in Mexico City
Same-sex marriage is legal in Mexico City —the Federal District of Mexico— having been approved by its Legislative Assembly on 21 December 2009, and signed into law by Head of Government Marcelo Ebrard on 29 December 2009...

 and parts of the United States
Same-sex marriage in the United States
The federal government does not recognize same-sex marriage in the United States, but such marriages are recognized by some individual states. The lack of federal recognition was codified in 1996 by the Defense of Marriage Act, before Massachusetts became the first state to grant marriage licenses...