Just two years ago, the Supreme Court struck down part of the federal anti-gay marriage law that denied a range of government benefits to legally married same-sex couples.

The decision in United States v. Windsor did not address the validity of state marriage bans, but courts across the country, with few exceptions, said its logic compelled them to invalidate state laws that prohibited gay and lesbian couples from marrying.

The number of states allowing same-sex marriage has grown rapidly. As recently as October, just over one-third of the states permitted same-sex marriage. Now, same-sex couples can marry in 36 states and the District of Columbia. A look at what is now before the Supreme Court, and the status of same-sex marriage around the country.

The justices on Tuesday are hearing extended arguments, scheduled to run 2½ hours, in highly anticipated cases about the right of same-sex couples to marry. The cases before the court come from Kentucky, Michigan, Ohio and Tennessee, all of which had their marriage bans upheld by the federal appeals court in Cincinnati in November. That appeals court is the only one that has ruled in favor of the states since the 2013 Windsor decision.