Argentina, Belgium, Canada, Spain, South Africa and Norway are among nearly a dozen countries that allow same-sex marriages.
Polls show the U.S. public has gradually become more accepting of the idea, with more Americans in favor in 2013 than opposed, according to Pew.
Nonetheless, 30 states have passed constitutional amendments banning same-sex marriage, according to the Pew Research Center.
The issue has also divided Australia, where lawmakers voted against a bill to legalize same-sex marriage last September. A poll for the advocacy group Australian Marriage Equality indicated that 64 percent of those surveyed "support marriage equality."
According to a report released in May 2011 by the International Lesbian, Gay, Bisexual, Trans and Intersex Association, same-sex relations are still criminalized in 76 countries, and in five of those countries, the death penalty can be applied to those who violate the laws.