Same-sex marriage (also called gay marriage) is a legally or socially recognized marriage between two persons of the same biological sex or social gender.
The Netherlands was the first country to legalize same-sex marriages, with the first marriages performed in the Amsterdam city hall on 1 April 2001. Since then, same-sex marriages have been legalized in Belgium (2003), Spain (2005), Canada (2005), South Africa (2006), Norway (2009), Sweden (2009), Portugal (2010), Iceland (2010), Argentina (2010), Denmark (2012), Brazil (2013), France (2013), Uruguay (2013), New Zealand (2013), the United Kingdom (2014), Luxembourg (2015), the United States (2015), Ireland (2015), Colombia (2016), and Finland (from 2017). In Mexico, same-sex marriages are legally recognized in all states but can only be performed in some. Israel recognizes same-sex marriages performed in other countries, but does not permit them to be performed in Israel itself. A number of other countries have announced plans to seek legalization of same-sex marriages, and some recognize same-sex civil unions, but not marriages.
An excerpt from the Supreme Court decision in Obergefell v. Hodges that legalized same-sex marriage in all 50 US states on June 26, 2015:
No union is more profound than marriage, for it embodies the highest ideals of love, fidelity, devotion, sacrifice, and family. In forming a marital union, two people become something greater than once they were. As some of the petitioners in these cases demonstrate, marriage embodies a love that may endure even past death. It would misunderstand these men and women to say they disrespect the idea of marriage. Their plea is that they do respect it, respect it so deeply that they seek to find its fulfillment for themselves. Their hope is not to be condemned to live in loneliness, excluded from one of civilization’s oldest institutions. They ask for equal dignity in the eyes of the law. The Constitution grants them that right. The judgment of the Court of Appeals for the Sixth Circuit is reversed. It is so ordered.