The Netherlands was the first country to legalize gay marriage in 2000.
The groundbreaking law also gave couples in the Netherlands the right to adopt children.
Belgium followed suit and passed gay marriage in 2003.
Three years after it legalized gay marriage, Belgium gave gay couples the right to adopt, according to Pew. Belgium has also outlawed employment discrimination based on sexual orientation.
Spain legalized gay marriage by a close margin in 2005.
Before it legalized same-sex marriage, Spain already banned employment discrimination against gays, according to a Harvard Law publication on the subject. In 2007, Spain passed a law that let people officially change their gender before going through a sex-change surgery.
Canada also passed gay marriage legislation in 2005.
Canada amended its human rights law all the way back in 1996 to ban discrimination based on sexual orientation.
South Africa became the first country in Africa to legalize gay marriage in 2006.
South Africa's ban on discrimination against gays in its 1994 post-apartheid constitution made it one of the first countries in the world to outlaw discrimination based on sexual orientation, according to the BBC.
Norway passed a law allowing gay couples to marry, adopt children, and have artificial insemination in 2009.
Norway has put pressure on the U.N. to ensure that all countries decriminalize homosexuality.
Sweden legalized same sex-marriage in 2009.
But same-sex couples have been allowed to register for civil unions since 1995, according to Pew.
Portugal became the eighth country to legalize same-sex marriage in 2010.
The New York Times' Frank Bruni has noted that Portugal's decision to legalize gay marriage is remarkable given that it's tiny and "overwhelmingly Roman Catholic."
The Icelandic parliament legalized same-sex marriage in 2010.
Iceland is also the only country in the world to have an openly gay head of state, Reuters has pointed out.
Argentina became the first country in Latin America to legalize gay marriage in 2010.
But the couple pictured here faced extreme opposition when they tried to marry. A judge tried to prevent them from marrying just days before their planned wedding in December 2009, according to Reuters.
Denmark legalized gay marriage in 2012, but has recognized same-sex domestic partnerships since 1989 (the first country in the world to do so).
Denmark requires the state church to perform gay weddings, according to Pew. It was the first country to allow civil unions in 1989.
Britain's House of Commons has passed a gay marriage bill, the first step on the road to fully legalizing same-sex marriages.
The International Lesbian, Gay, Bisexual and Trans and Intersex Association (ILGA) ranked the U.K. the best country in Europe to be gay.
The German parliament is currently debating whether gay couples in a legal partnership should have the same full rights as heterosexual married couples.
A recent poll found that two-thirds of Germans support gay marriage, The New York Times reported in February.
