Ten years ago, CHARLES KAISER wrote The Gay Metropolis, the landmark portrait of 20th-century New York viewed through the eyes of gay New Yorkers. A lot has changed since then, from the murder of a Wyoming teenager named Matthew Shepard that reanimated the gay political movement, to the Supreme Court decision that is the most important event in the gay-rights struggle since the Stonewall riots in 1969. Later this month, Grove Press will publish a 10th-anniversary edition of the book. This article is adapted from the new afterword, in which Mr. Kaiser guides us through the amazing changes in gay life at the dawn of the new millennium.

At the dawn of the 21st century, gay life’s imprint on everyday life exploded as America embraced everything from the first gay mega-hit in prime-time television to the first gay Hollywood movie to capture universal acclaim—and collect $178 million at the box office.

When Will and Grace debuted in 1998, there was no indication that it might change the cultural landscape. As America’s first almost completely gay sitcom, it got off to a slow start, despite the presence of two straight women as two of the main characters. Even office workers in hip Manhattan were a little nervous about it: What would people think if they started to laugh at those jokes in front of the water cooler? But the quality of the humor gradually won them over. Beginning with its third season, the program attracted more than 17 million viewers every week, and it became the second-highest-rated sitcom among young adults for five years in a row. With the even more popular (and equally gay-friendly) Friends as its lead-in on Thursday nights, Will and Grace gradually appropriated a larger space in American pop culture than anything gay ever had before. Some critics carped that its characters were clichés, but many more decided that the show’s sharp writing placed it within the pantheon of great American sitcoms.

The success of Will and Grace opened the market up to all kinds of gay entertainment; it also gave a few celebrities the courage to finally proclaim who they really were. In 2002, Rosie O’Donnell confirmed one of the worst-kept secrets in show business when her autobiography revealed that she was a lesbian. Ellen DeGeneres had made the same revelation about herself on her own show, Ellen, five years earlier, but the mini-media event she created around her announcement (which included the cover of Time) was not enough to prevent the cancellation of her sitcom a year later. But her TV career began to take off again after she hosted the Emmy Awards following the attacks of 9/11.

She reminded the audience that they were supposed to go on with their lives as usual, because to do otherwise “is to let the terrorists win—and really, what would upset the Taliban more than a gay woman wearing a suit in front of a room full of Jews?” (Imagine someone saying that in prime time, 30 years ago.)

Will and Grace didn’t just change the landscape of American TV—by the end of its original run it had also been broadcast in more than 30 other countries, including France, Germany, Croatia, Pakistan, Sweden and Bosnia and Herzegovina. But just five months after its American debut, a new show started across the Atlantic which made Will and Grace look almost as tame as The Love Boat.

Created by veteran English television writer Russell T. Davies, Queer As Folk inspired a tsunami of criticism when it burst out from Britain’s Channel Four in 1999 with an opening episode which showed a 29-year-old man making very explicit love to a beautiful 15-year-old boy. The same installment featured the same 29-year-old at the birth of his son to a lesbian friend. After the 29-year-old bragged about his teenage conquest in front of the mother of his child, a woman friend observed: “So: You’ve both had a child this evening!”

The principal characters were young gay men in Manchester who were frankly sexual, extremely drug-friendly and never the least bit apologetic about any of it. Sarah Lyall of The New York Times called the show “an explosion of graphic language, male nudity and explicit sex guaranteed to offend as many people as it enthralled.” Gay activists were angered by the reinforcement of gay stereotypes (Mr. Davies called these critics “boneheaded, politically correct gay political fossils”) while straight viewers were squeamish with the reality that every gay adult begins life as a gay child. The fact that gay teenagers often seek out their first sexual experience with someone older was something else most people didn’t want to be reminded of in prime time.

From explicit gay sex on pay cable, it was a very short hop to the much tamer Queer Eye for the Straight Guy, a show which argued that there were no shortcomings in a straight geek that couldn’t be cured by the superior savoir-faire of five gay tastemakers. (The show also marked the final reclamation of the previously pejorative word “queer” by the gay community.) In 2005, MTV Networks launched Logo, a Viacom-owned gay cable channel, which quickly made distribution deals with every major cable and satellite network. Suddenly, American kids in 25 million homes had access to gay programming whenever they wanted it—at least when their parents weren’t watching them.

WITH SO MUCH INCREASED VISIBILITY FOR EVERYTHING GAY, the world was primed for another cultural breakthrough. In 2006, there were nine big movies with gay themes or gay characters, but only one caused a sensation. Brokeback Mountain was an A-list Hollywood feature that presented two gay cowboys as a perfectly normal part of Wyoming in the 1960’s—and that depiction of these archetypes of American masculinity turned out to be revolutionary all by itself. It was also the first gay love story on film that felt so universal, the enthusiasm of the audience wasn’t dampened by the sexual orientation of the principals.

The kind of movie that would have caused an uproar 20 years earlier became newsworthy because it provoked hardly any attacks. “What if they held a culture war and no one fired a shot?” Frank Rich asked. There was almost “no controversy, no Fox News tar and feathering, no roar from the religious right”—and the film won three Academy Awards, including Best Director and Best Adapted Screenplay.

A crucial element in the movement’s steady progress was a simple matter of demographics: Since the 1960’s, every new generation of Americans has been more accepting of sexual diversity than the one before it. Although harassment of openly gay high-school students remains rampant, every year there is a growing number of young men and women who are coming out to their parents and their friends long before they reach college.

Besides exposing their peers to proud young gays and lesbians at an early age, these brash young men and women make another significant contribution. In many cases, the first gay people American adults meet are the gay classmates that their straight children bring home with them from high school.

“This has brought gay people into households all over America,” said Matt Coles, the head of the gay-rights project at the ACLU. “The important thing is not just knowing someone gay, but talking to someone who is gay. I think they’re having really important dialogues with their friends’ parents.”

GAY MARRIAGE GOT MORE ATTENTION THAN ANY OTHER issue, partly because it inspired the most vehement opposition. Some gay activists would have preferred to move more slowly on this hot-button subject, but two state courts bumped it to the front of the national agenda. In 1999, the Vermont Supreme Court ruled that same-sex couples were entitled to the same rights as heterosexual couples. Four months later, Governor Howard Dean signed a civil-union bill which made Vermont the first state in the union to give same-sex couples the same rights as married men and women—without calling it marriage.

In the spring of 2001, seven gay couples who had been denied marriage licenses in Massachusetts filed a lawsuit demanding the right to marry. Two and a half years later the Massachusetts Supreme Court declared that the state constitution required marriage equality for same-sex couples. When the same court bolstered that ruling with another one early in 2004 that required the state legislature to enact full marriage rights for same-sex couples, it sparked a series of events that kept the issue at the top of the national agenda for the rest of the year.

Eight days after the second court decision in Massachusetts, San Francisco Mayor Gavin Newsom decided that California’s constitution authorized him to immediately start marrying same-sex couples. Within days, more than 2,000 couples were issued marriage licenses, and newscasts all across the country were flooded with images of happy couples lined up on the steps of San Francisco’s City Hall to formalize their relationships.

The California Supreme Court eventually invalidated all of those marriages, but the combination of the mayor’s edict and the Massachusetts decision triggered a firestorm of opposition from the religious right.

George Bush catered to his evangelical base by endorsing a federal constitutional amendment to ban gay marriage, 12 days after the marriages in San Francisco began.

In March, the House and Senate both held hearings on the proposed amendment, but it was defeated in the Senate by vote of 49 to 48. In May, 600 same-sex couples applied for marriage licenses the first day they were available in Massachusetts. Meanwhile, allies of the President petitioned to get state constitutional amendments banning same-sex marriage on the ballot in 11 states: Arkansas, Georgia, Kentucky, Michigan, Mississippi, Montana, North Dakota, Ohio, Oklahoma, Oregon and Utah.

Conservatives argued that gay marriage threatened heterosexual unions, but no one ever offered a credible explanation of why that might be so. As gay Congressman Barney Frank asked when the debate first began to catch fire, if gay marriage were legalized, were married men across America “really going to smack themselves on the head, and say, ‘Wow! I could I have married a man!’”

Nevertheless, every one of those anti-gay-marriage amendments passed easily that November. And when voters were asked in a national exit poll which issue mattered most in deciding their vote for President, 22 percent chose “moral values” as their first choice. Those facts produced an instant consensus: Opposition to gay marriage had played a decisive role in George Bush’s re-election. But a closer examination of the election’s results revealed there was no hard evidence to support that notion.

Ethan Geto, the New York politico who began the fight for gay rights way back in 1970 in the Bronx, sat down in 2005 to examine what had really happened the previous November. He discovered that voters who cited “moral values” as their primary concern—who were then asked follow-up questions—cited everything from Janet Jackson’s breast-baring at the Super Bowl to “commercials selling products you don’t want your children to see” as the moral values they were talking about. For many evangelical Christians—the most reliable opponents of gay marriage—the main component of moral values was their antipathy to abortion.

Humphrey Taylor, the chairman of the Harris Interactive Poll, noted that when people were asked to say what they thought were the most important issues without prompting and without being shown a list, “the overwhelming majority of people mentioned the war on terror, Iraq, the economy, jobs, health care and education. Many people chose moral values [from a list] because it is the right thing to say.” And when a post-election poll by Zogby International asked “Which moral issue most influenced your vote?”, gay marriage came in last, at 9 percent, far behind the war in Iraq, at 42 percent.

On the question of whether the gay initiatives had helped to re-elect President Bush, Mr. Geto’s analysis was even more convincing. Only New Mexico and Iowa switched to Bush in 2004, and neither of them had anti-marriage proposals on the ballot. On the other hand, in three key swing states that did have gay-marriage initiatives—Michigan, Ohio and Oregon–Senator John Kerry (in 2004) outperformed Vice President Al Gore (in 2000) in all three. Although neither Mr. Gore nor Mr. Kerry carried the key state of Ohio, Mr. Kerry came two points closer to a win than Mr. Gore.

And according to Alan Abramowitz of Emory University, Mr. Bush’s share of the vote in states without the initiatives increased by 2.9 percent between 2000 and 2004, but only by 2.6 percent in the states that did have them.

WHILE THE TIDE AGAINST GAY MARRIAGE SEEMED TO BE prevailing at the polls, another wave was going in the opposite direction. Shortly after Vermont approved civil unions for gay couples, Tom Stoddard’s old dream of gay wedding announcements in The New York Times came true. On Aug. 18, 2002—nine years after Stoddard, a great gay activist, first lobbied for the change—the paper announced its “Weddings” pages would become “Weddings/Celebrations.” Two weeks later, the paper reported the union in Vermont of Daniel Gross and Steven Goldstein—the owner of a public-affairs consulting firm and a vice president of GE Capital. (When I sent Times publisher Arthur Sulzberger Jr. a note congratulating him on the change, he replied with one word: “Overdue.”)

Today more than 500 papers around the country print same-sex wedding announcements, including six in Alabama, 58 in California, seven in Maine and 31 in Texas.

A poll for the Pew Research Center found the number of Americans who “strongly opposed” gay marriage dropped sharply from 42 percent in 2004 to just 28 percent in 2006 (and just 25 percent among Americans younger than 29).

“I think that two generations from now it will be over,” said Mr. Coles of the ACLU—and gay marriage will become legal in America?! “Right now the states fall into four categories: One is Massachusetts, with marriage; four in the second category—Vermont, Connecticut, California and New Jersey—have strong domestic-partnership laws; Hawaii and Maine are in category three—with some significant legal protection; and then there is a fourth category of states that have non-discrimination laws.

“In 25 years, about 30 states will have either marriage or complete civil unions,” Mr. Coles continued, “and then the momentum for nationwide recognition will become pretty much irresistible. Most of the country’s corporate establishment will want it; because it will be too much of a pain in the ass for them, because their employees won’t work in states that don’t recognize them. They’ll be on our side.” (At the end of 2006, 138 major U.S. corporations got a rating of 100 percent from the Human Rights Campaign for the benefits and protections they had extended to their gay employees.)

AS AMERICA SEESAWED BACK AND FORTH ON THE QUESTION of gay marriage, one event was vastly more important than all the others in the fight for equal rights in the new millennium. It was yet another watershed which Stoddard had prophesied 20 years earlier.

Back in 1986, the United States Supreme Court had handed the gay movement its greatest defeat since its birth in the Stonewall riots of 1969 in Greenwich Village. Against the expectations of most court experts, it affirmed a Georgia law which prohibited sodomy between consenting adults inside their own homes. Writing for the 5-to-4 majority in Bowers v. Hardwick, Associate Justice Byron White asserted that to claim that a right to engage in sodomy was “‘implicit in the concept of ordered liberty’ is, at best, facetious.” Stoddard called the case the movement’s “Dred Scott decision”—comparing it to the 1857 Supreme Court ruling which held that blacks were not citizens and therefore could be slaves. And Stoddard was certain that the fierce minority opinion written by Justice Harry Blackmun would one day become the law of the land. Blackmun argued that the case was really about “the right most valued by civilized men,” which he identified “as the right to be let alone.”

A year after Bowers v. Hardwick, Ronald Reagan tried to move the court sharply to the right by nominating Robert Bork to be a Supreme Court Justice. After a fierce battle in the Senate, his nomination was rejected by a vote of 58 to 42. Anthony Kennedy was then nominated and confirmed for the same opening. Five years later, in 1992, Bill Clinton became the first President to be elected with the active support of the gay community. He then nominated Ruth Bader Ginsburg and Stephen Breyer to the Supreme Court, and the Senate confirmed them in 1993 and 1994, respectively. Together, these four events set the stage for the single greatest triumph of the gay-rights movement in America.

In 2002, the Supreme Court agreed to hear an appeal in the case of Lawrence v. Texas. The facts of the case were quite similar to Bowers v. Hardwick. As in the earlier case, two men—John Geddes Lawrence and Tyron Garner—had been arrested inside a private home by a policeman who had discovered them in bed together. Gay-rights attorneys had been searching for the best case to bring before the court to overturn the Bowers v. Hardwick precedent, and Lawrence seemed to provide the perfect opportunity to do that. This time the challenge was to the anti-sodomy law in Texas.

On June 26, 2003, the Supreme Court issued the decision that every gay activist had been waiting for since the birth of the movement. The 6-to-3 decision was written by Justice Kennedy. The majority had been made possible by Justice Kennedy and the two justices appointed by Bill Clinton, the most gay-friendly President in history. This made it a triumph of politics, as well as common sense.

It overruled the Texas law in the broadest way possible. It also apologized for the Bowers v. Hardwick decision with unprecedented directness. Linda Greenhouse, the veteran Supreme Court correspondent for The New York Times, specified the singular importance of the decision: “A conservative Supreme Court has now identified the gay rights cause as a basic civil rights issue.”

The court had reversed itself many times on many other subjects, including segregation. But never before had it used such sweeping language to repudiate a previous precedent. “Bowers was not correct when it was decided, and it is not correct today,” Justice Kennedy wrote. “It ought not to remain binding precedent. Bowers v. Hardwick should be and now is overruled …. Its continuance as precedent demeans the lives of homosexual persons.”

To Mr. Coles, Lawrence was for gay people what Brown v. Board of Education had been for black people: the single most important legal event in the history of their struggle. With a stroke of the pen, the court had struck down all 13 of the remaining state laws which had made the way gay people make love a crime:

“Freedom extends beyond spatial bounds,” Justice Kennedy wrote. “Liberty presumes an autonomy of self that includes freedom of thought, belief, expression, and certain intimate conduct. The instant case involves liberty of the person both in its spatial and more transcendent dimensions.”

“It suffices for us to acknowledge that adults may choose to enter upon this relationship in the confines of their homes and their own private lives and still retain their dignity as free persons. When sexuality finds overt expression in intimate conduct with another person, the conduct can be but one element in a personal bond that is more enduring. The liberty protected by the Constitution allows homosexual persons the right to make this choice.”

“When homosexual conduct is made criminal by the law of the State, that declaration in and of itself is an invitation to subject homosexual persons to discrimination both in the public and in the private spheres.”

“The petitioners are entitled to respect for their private lives. The State cannot demean their existence or control their destiny by making their private sexual conduct a crime. Their right to liberty under the Due Process Clause gives them the full right to engage in their conduct without intervention of the government. ‘It is a promise of the Constitution that there is a realm of personal liberty which the government may not enter.’”

“Had those who drew and ratified the Due Process Clauses of the Fifth Amendment or the Fourteenth Amendment known the components of liberty in its manifold possibilities, they might have been more specific. They did not presume to have this insight. They knew times can blind us to certain truths and later generations can see that laws once thought necessary and proper in fact serve only to oppress. As the Constitution endures, persons in every generation can invoke its principles in their own search for greater freedom.”

With this revolutionary opinion, Justice Kennedy had transformed the status of gay people forever. And he had done so in the wisest way possible: He had broadened the definition of liberty in America for everyone.