By ALEX WILLIAMS

WHEN Newt Gingrich’s second wife, Marianne, jolted the Republican race with her recent claim that the presidential hopeful had once asked for, in her words, an “open marriage,” the phrase seemed like an echo from the Nixon years. “Open marriage”? Adjust the rabbit ears. What decade are we in?

 The idea of trying a nonmonogamous marriage by mutual consent enjoyed a brief cultural vogue, along with encounter groups and key parties, after the publication of the best-selling book “Open Marriage: A New Life Style for Couples,” by Nena and George O’Neill, in 1972. But once the AIDS epidemic hit, talk of open marriage seemed to vanish in polite circles.

“The 1980s and much of the 1990s saw an almost complete eradication of the term ‘open marriage’ from public discourse,” said Dr. Curtis R. Bergstrand, an associate professor of sociology at Bellarmine University in Louisville, Ky., who recently wrote a book on the practice. Even to evoke the term nowadays sounds, to many, a little dated, like referring to your wife as your “lady” or to a band as a “group.”

But like Mr. Gingrich himself, the concept has popped up again, and not just as an unlikely topic in primary-season discourse. The phrase has become a titillating staple of celebrity gossip headlines. And the idea of the open relationship, supported by Web sites and a new generation of books, is showing signs of a second life as an alternative-sexual subculture for a generation acclimated to high divorce rates, Dr. Bergstrand said.

Many are latchkey children of the Generation X-cliché variety who grew up after the sexual revolution, when divorce had become routine and alternative sexual options, like bisexuality, have become more socially accepted.

If nothing else, Marianne Gingrich’s allegation, which the candidate has denied, provided an unexpected publicity bounce for advocates of open relationships, who have long been trying to paw their way out of the cultural margins.

“We could never afford this kind of a public-relations opportunity,” said Anita Wagner Illig, an organizer of the Polyamory Leadership Network, an online organization advocating nonmonogamous relationships. She was interviewed by the BBC and Washington’s ABC news affiliate after the statements by Marianne Gingrich, and traffic at ModernPoly.com, an advocacy Web site promoting open relationships, spiked nearly 30 percent in the weeks that followed.

Though Mr. Gingrich’s candidacy unintentionally helped reintroduce the topic of open marriages in mainstream conversation, no one in the subculture appears to be embracing him as a celebrity spokesman.

As Ms. Gingrich told reporters, her ex-husband asked for an open marriage, though not in those exact words, after a counseling session so he could continue to see another woman, Callista Bisek, to whom he is now married (a story Mr. Gingrich angrily refuted). Advocates go to great pains to dispel the idea that open marriage, at least when practiced responsibly, is just a handy after-the-fact excuse for wandering spouses.

“Cheating while married can technically fall under polyamory since it does mean ‘many loves,’ ” said Birgitte Philippides, a New York makeup artist and former president of Polyamorous NYC. “However, people in the polyamory movement don’t usually like to look at it that way. They think cheating is just cheating.”

As practiced today, open-marriage arrangements can take many forms. Some fall under the rubric of polyamory, which involves a couple sharing emotional and romantic attachment, as well as sexual, with more than one person. (Not all polyamorists are married, however, and many relationships involve bisexuality.)

 Some fall under the term “partnered nonmonogamy,” which involves outside sexual relationships, but no emotional attachment, said Tristan Taormino, the author of “Opening Up,” a 2008 survey of 100 nonmonogamous relationships in this country that includes advice on managing jealousy and parenting duties for latter-day Bobs and Carols and Teds and Alices.

 Despite the whiff of Roman-scale hedonism, modern open marriages often have little to do with the swinging sex romps of the “Love the One You’re With” era. Ground rules are usually settled on in advance by all parties. Some even sign family contracts delineating financial obligations, said Diana Adams, a New York lawyer and practicing polyamorist. Others seek to lend the practice an air of legitimacy by using terminology like the lawyerly “negotiated monogamy.”

 In some cases, sex is beside the point. The cartoonist Robert Crumb and his wife, Aline Kominsky-Crumb, have been outspoken in the past about keeping other partners on the side. But, Ms. Kominsky-Crumb said in one interview, “We’re old and not as sex driven as we once were.” Her “second husband” (whom she says she no longer sees) came in most handy when she needed “somebody to do the ‘man’ things that Robert can’t do, such as fix the plumbing or drive a car.”

 What exactly constitutes “sex” has changed, too. Technology has played a major role in increasing awareness of relationship options for a new generation, said Janet W. Hardy, who wrote, with Dossie Easton, “The Ethical Slut,” a 1997 book advocating nonmonogamous relationships that has sold more than 100,000 copies (a second edition was published in 2009).

Online culture brings new opportunities to engage with other partners outside the traditional bounds of monogamy, whether they are hookups on Craigslist or flirtatious “direct messages” on Twitter, Ms. Hardy said. But more important, it allows polyamorists a means to find one another and trade strategies for maintaining workable open relationships.

In the first flush of open marriage in the ’70s, there was hardly any way for the curious to find like-minded people. “Then the Internet came along and it was all just a keystroke away,” she said, adding that there are dozens of online forums devoted to the practice today. “It turned from an oddity into a community.”

 And in Hollywood (where the bonds of marriage are often junk grade), it is not uncommon for celebrities to muse on the idea, however hypothetically, in interviews.

 The actress Mo’Nique made headlines in 2010 when she told Barbara Walters that “it would not be a deal-breaker” if her husband, Sidney Hicks, had sex outside their marriage. “What if it’s 20 times?” the star of the film “Precious” was quoted as saying. “So what?”

“We’ve been best friends for ... is it over 25 years? And we truly know who we are,” she said. “Truly.”

   Even the homespun Dolly Parton, the polar opposite of Hollywood values, inspired tabloid speculation after an interview with a British newspaper in 2007. “I don’t want to know it, if he’s cheating on me,” she said of her longtime husband, Carl Dean. “If I’m cheating on him, he wouldn’t want to know it. And if we do, if that’s what’s making it work, then that’s fine, too.”

(She later told Oprah the much-repeated comments were taken out of context. “That just means we let each other be who we are and how we are. But I’d kill him if I knew he was with somebody,” she joked.)

  It has reached the point that whenever any Hollywood power couple displays fissures, rumors (like lawyers) soon follow. After Ashton Kutcher’s and Demi Moore’s recent split, Chelsea Handler speculated on Piers Morgan’s CNN show about their marital boundaries. “I don’t know them personally very well,” she said. Not letting that stop her, she added, “But I think it’s pretty obvious that they probably had a lot of open marriage-type situations.”

 All of which raises this question: How many people are actually trying this? Even academics who study sexuality have no idea, since most practitioners remain in the closet, fearing bias, said Dr. Elisabeth Sheff, an assistant professor of sociology at Georgia State University and author of a forthcoming study on polyamory in America.

 And good luck finding out from the subculture’s leadership, which is loosely organized at best, said Ms. Illig of the Polyamory Leadership Network. And no wonder, she added. “We don’t have much time for it with multiple partnerships to see to.”

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