1996: Congress passed the Defense of Marriage Act, which prohibited the federal government from recognizing same-sex marriages. No state at that time allowed marriage between two men or two women.
1998: The Kentucky General Assembly approved House Bill 13, defining marriage as exclusively between one man and one woman.
2000: Vermont became the first state to allow "civil unions" for same-sex couples, with most of the legal rights of marriage.
2003: Massachusetts became the first state to allow same-sex couples to marry, following a decision by its highest state court.
2004: Nearly 75 percent of Kentucky voters approved a state constitutional amendment to provide that "only a marriage between one man and one woman shall be a marriage in Kentucky." The amendment also banned recognition of same-sex civil unions.
June 2013: The U.S. Supreme Court struck down the Defense of Marriage Act, or DOMA, in a case called United States vs. Windsor. Ruling 5-4, the court said DOMA interfered with the state of New York's right to recognize same-sex marriage, as it had since 2011. The decision so strongly criticized the language of DOMA — saying it served "no legitimate purpose" other than anti-gay discrimination — that marriage-equality advocates saw it as an invitation to challenge marriage bans in dozens of states.
July 2013: Four same-sex couples in Louisville sued Gov. Steve Beshear in a case called Bourke vs. Beshear. They wanted Kentucky to recognize their same-sex marriages, all legally performed elsewhere.
February 2014: U.S. District Judge John G. Heyburn II in Louisville ruled in favor of the same-sex couples in Bourke vs. Beshear and partially struck down Kentucky's same-sex marriage ban, ruling that out-of-state marriages must be recognized. Heyburn put his order on hold pending the state's appeal. Two days later, a second lawsuit was filed before Heyburn, Love vs. Beshear, asking that Kentucky issue its own marriage licenses to same-sex couples.
July: Heyburn likewise ruled for the same-sex couples in Love vs. Beshear, eliminating Kentucky's same-sex marriage ban entirely. But he again put his order on hold pending the state's appeal.
August: Kentucky joined three other states — Tennessee, Ohio and Michigan — in arguing for their same-sex marriage bans before the 6th Circuit U.S. Court of Appeals in Cincinnati. Federal district judges in all four states had struck down the bans as unconstitutional.
October: The U.S. Supreme Court refused to "grant cert" — to review — seven petitions arising from successful challenges to state marriage bans. This preserved the unanimous circuit court decisions striking down bans in Indiana, Wisconsin, Utah, Oklahoma and Virginia and other states with similar bans in those circuits. Within six months, 37 states would recognize same-sex marriage.
November: In a 2-1 ruling, the 6th Circuit reversed the lower courts' decisions in Kentucky, Tennessee, Ohio and Michigan. It became the first federal appeals court to uphold a state's right to ban same-sex marriage.
January: With a split in the circuits, the Supreme Court agreed to review the 6th Circuit's decision. The high court said it would consider two constitutional questions: Does the 14th Amendment require a state to issue a marriage license to same-sex couples? And does it require a state to recognize a same-sex marriage that was lawfully performed in another place where such marriages are legal?
April 28: The Supreme Court hears arguments in Obergefell vs. Hodges, the formal name of the combined same-sex marriage suits from Kentucky, Tennessee, Ohio and Michigan. A decision is expected this summer.