The ruling was made official in a 5-4 vote by the U.S. Supreme Court.
Prior to the ruling, same sex marriage had been legal in 37 states. The states in red are where same-sex marriage will now be legal.
Same-sex marriage supporters across the United States expressed their joy in reaction to the ruling.
PHOTOS: Reactions to U.S. Supreme Court ruling on same-sex marriage
President Obama addressed the ruling in a press conference on Friday, calling the ruling a "victory for America."
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— President Obama (@POTUS) June 26, 2015