As the U.S. Supreme Court prepares to weigh two cases dealing with gay marriage, here's a look at how the debate has touched American life over the last four decades:
In Baker v. Nelson, the U.S. Supreme Court dismisses a challenge of a ruling from Minnesota that gay couples have no constitutional right to marry, saying the appeal fails to raise a "substantial federal question."
Maryland becomes the first state to define marriage as a union of one man and one woman.
The American Psychiatric Association removes homosexuality from its list of mental disorders.
PBS runs An American Family, an early reality show that follows the life of the Loud family, including openly gay Lance Loud.
Gay activist Harvey Milk is elected to San Francisco's Board of Supervisors (and assassinated a year later).
Anita Bryant launches a campaign against expanding gay rights, called Save Our Children, with the slogan "Homosexuals cannot reproduce, so they must recruit."
What will be known as the AIDS crisis begins, becoming a focus for many gay activists.
Wisconsin becomes the first state to outlaw discrimination based on sexual orientation. More than 20 states eventually follow suit.
In Bowers v. Hardwick, the U.S. Supreme Court rules that the Constitution does not protect the right of gay adults to engage in consensual sodomy in private.
TV's The Golden Girls take on gay marriage in an episode, as Blanche's brother plans to marry his boyfriend.
The Hawaii Supreme Court rules a ban on gay marriage may violate its constitution, but is stripped of jurisdiction over the matter by a constitutional amendment five years later.
The Pentagon's "don't ask, don't tell" policy takes effect.
Tom Hanks portrays a gay man with AIDS in Philadelphia — and later wins an Oscar.
Pedro Zamora, a cast member on MTV's The Real World: San Francisco, and his boyfriend exchange rings in a ceremony shown on air. Zamora dies of AIDS shortly after the series ends.
Two male characters who run a bed-and-breakfast get married on CBS' Northern Exposure.
Wilson Cruz portrays a gay teenager on ABC's My So-Called Life.
Utah passes a law prohibiting same-sex marriage. More than 30 other states will follow with so-called Defense of Marriage laws.
In Romer v. Evans, the U.S. Supreme Court strikes down a Colorado constitutional amendment that had forbidden laws banning discrimination against gays.
President Clinton signs a federal Defense of Marriage Act.
Gallup begins tracking public opinion on legalizing same-sex marriage.
Ellen DeGeneres comes out in real life and on her TV sitcom, with more than 40 million people watching. In 2008, she marries actress Portia de Rossi in California.
After an Alaska Superior Court judge rules same-sex couples have a right to marry in the state, voters approve a constitutional amendment banning gay marriage. More than 20 states will follow.
Tammy Baldwin of Wisconsin becomes the first openly gay non-incumbent to be elected to Congress.
Gay teen Matthew Shepard is murdered in Wyoming.
Will & Grace, a sitcom following the love lives of a gay male lead character and his straight female best friend, debuts.
Vermont becomes the first state to legalize same-sex civil unions.
The U.S. Supreme Court overturns its 1986 Bowers v. Hardwick decision, ruling gays are "entitled to respect for their private lives," and strikes down a Texas sodomy law in Lawrence v. Texas.
The Massachusetts Supreme Judicial Court rules in favor of same-sex marriage.
Early in the year, a few local governments around the country grant marriage licenses or officiate weddings for same-sex couples before being halted by the courts.
Same-sex couples legally marry for the first time in Massachusetts.
Thirteen states pass constitutional amendments banning gay marriage, and some Republicans, including President George W. Bush, call for amending the U.S. Constitution.
New Jersey's Supreme Court rules gay couples are entitled to the same rights as heterosexual couples; the Legislature opts to legalize civil unions.
Eight states pass constitutional amendments banning gay marriage.
Democratic presidential candidates participate in forum on gay issues on Logo TV.
Connecticut's Supreme Court rules same-sex couples have a right to marry.
California's Supreme Court overturns that state's gay marriage ban in May, legalizing same-sex marriage, but voters approve a constitutional amendment in November to end gay marriage.
Legislators in Vermont, New Hampshire and Washington, D.C., legalize gay marriage. The Iowa Supreme Court strikes down the state's ban, legalizing same-sex marriage there.
New York's Legislature approves gay marriage.
The Pentagon's "don't ask, don't tell" policy is repealed.
Maine, Maryland and Washington become the first states where voters legalize gay marriage.
President Obama becomes the first sitting president to endorse same-sex marriage.
Jay-Z and several other prominent hip-hop figures talk about their support for gay marriage.
The U.S. Supreme Court announces it will hear challenges to the federal Defense of Marriage Act and California's ban on same-sex marriage.
Compiled by Erica Ryan. Audio interviews conducted in March 2013 by Ari Shapiro.
Sources: SCOTUSblog, PBS, IMDb, Gallup, the National Conference of State Legislatures, the Pew Forum on Religion and Public Life, NPR