On Friday Ireland could become the first country to approve same-sex marriage through a popular vote. If the yes campaign prevails in the referendum, Ireland would become the 18th country to allow same-sex couples to marry.
In 2001 the Netherlands became the first country to legalise same-sex marriages. The first ceremony took place just after midnight on 1 April.
Denmark led the way on civil partnerships, introducing them for same-sex couples in 1989, but gay marriage only became legal there in June 2012.
At the turn of this year Luxembourg became the latest country to legalise same-sex marriage. Laws pending in Slovenia and Finland are expected to come into effect this year and in 2017 respectively.
In the US, two years ago it was legal in six states plus the District of Columbia, covering 11% of the population. Today 37 states plus the capital district allow it, which means nearly 72% of the US population live in a state that can issue a marriage licence to a same-sex couple, according to the Freedom to Marry campaign.
The absolutely stunning rise in support for gay marriage, in 1 chart http://t.co/IB1NZ72eq8 pic.twitter.com/geAUXgVj7m
— Chris Cillizza (@TheFix) May 20, 2015
South Africa remains the only African country where same-sex marriage is legal, and no countries in Asia have enshrined in law.
In the UK there were 1,409 same-sex marriages in the first four months after it became legal in 2014, according to the Office for National Statistics. More than half (56%) of the weddings were between female couples.
Research by the International Lesbian and Gay Association (Ilga), published in May 2014, found that more than 2.7 billion people live in countries where being gay is a crime. It said being lesbian, gay, bisexual or transgender was illegal in almost 80 countries, and in at least five of these it was punishable by death.
• This article was amended on 26 May 2015. An earlier version of the graphic failed to include France among the countries where same-sex couples can marry.
