In a landmark decision on June 26, 2015, the Supreme Court ruled that the Constitution guarantees a right to same-sex marriage. The deciding vote in the 5-4 ruling, Justice Kennedy said, “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.”Before the decision, 13 states still refused to recognize gay marriage. President Obama Tweeted, "Today is a big step in our march toward equality. Gay and lesbian couples now have the right to marry, just like anyone else. #LoveWins"
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A bill to legalize same-sex marriage was passed by an overwhelming majority by the Members of the Scottish Parliament (105-18) on February 4, 2014 and will be fast-tracked to implementation with the first same-sex marriages expected to be carried out in mid-to-late 2014.(Source) see more on Scotland
UPDATE: On July 17, 2013 the House of Commons and the House of Lords signed off on a bill that legalizes same-sex marriage. Following that, the bill was given the royal assent by the Queen, which means the law is officially official.see more on United Kingdom