To many, "open marriage" is a phrase so laden with 1970s nostalgia that the idea can't be considered without imagining its practitioners leering at each other across shag-carpeted conversation pits, their chest hair spilling out of maroon polyester leisure suits.
While many of today's adherents are aging swingers from the old school, a new generation -- well organized and committed to legitimizing a lifestyle -- continues to push traditional notions of marital fidelity by having sex with people other than their spouses.
But do marriages -- fragile institutions traditionally built on the fidelity and sexual intimacy of two people -- work when the doors of the bedroom are thrown wide open?
"That's like asking if monogamy works," Deborah Anapol, a psychologist and author of "Polyamory: The New Love Without Limits" told ABC NEWS.com. "Sometimes it does, and sometimes it doesn't. It depends almost entirely on the people involved and their willingness to tell the truth and do the work."
"Polyamory," which literally means "many loves" is a new name for an old practice.
"There were a few studies on open marriage in the early '60s and '70s, but the phenomenon seemed to die out and it was just called cheating after that," said William Doherty, a professor of sociology at the University of Minnesota.
"It resurfaced as polyamory, and some groups have imbued it with a spiritual side. They see it as a pathway to personal development. They see it as a high road; it's not cheating, it's growing their relationship," he said.
In 1972, George and Nena O'Neill published "Open Marriage: Love Without Limits," the first book to define the practice and counsel couples on how to grow their own relationships by creating friendships and sexual relationships with other people.
Ten years later, acclaimed journalist Gay Talese would publish "Thy Neighbor's Wife," an experiential look at American sexual mores between the sexual revolution and the AIDS epidemic.
In the book, Talese describes operating a massage parlor in New York City, attending nudist camps and having an extramarital affair.
Though Talese told ABC NEWS.com that his 50-year marriage to his wife, book editor Nan Talese, was not open, the popularity of "Thy Neighbor's Wife" led many Americans to re-evaluate long held ideas about sexual morality, obscenity and fidelity.
It is difficult to determine just how many married people are involved in open marriages. A study from the 1980s suggested it could be as many as 6 percent of all couples, but most experts believe that number is excessively high.
"At least 95 percent of married and cohabitating Americans expect sexual exclusivity," said Judy Treas, a sociology professor at the University of California at Irvine.
As for the success of open marriages, "there have been no scientific evaluations of how well open marriages work," Treas said. "The jury is still out."
Despite the small niche, there is a thriving industry built around the polyamorous. Self-help books, specialized marriage counselors, and retreats, which include everything from courses in Eastern philosophy to the chance to hook up with strangers, are targeted at people in open marriages.
Traditional marriage counselors typically tell polyamorous couples who are having problems with their marriage that it is the sex with other people that is causing their problems, but therapists like Dossie Easton who co-wrote"The Ethical Slut," disagreed.
Easton said polyamorous marriages were no more or less successful than monogamous marriages, but at least the polyamorous were never surprised to learn their spouse was cheating.
She said openly married couples saw her "for the same problems that traditional therapists deal with. Only traditional therapists tell polyamorous couples if they gave up being polyamorous, then they'd be happy."
Problems, she said, occur when spouses have different ideas about how polyamory should work.
"Sometimes one wants to have sex with strangers, and the other wants more meaningful relationships outside the marriage. Others want to join groups of likeminded people, [which] I call pods or constellations, where sometimes child-rearing responsibilities are shared."
The biggest challenge polyamorous couples seem to face is jealousy.
A whole chapter of "Open Marriage," the first polyamorous handbook is devoted to managing feelings of jealousy.
"Jealousy is inevitable just like anger is inevitable. All couples get jealous often for no good reason, but jealousy can be managed. If people are emotionally intelligent they work to manage their jealousy," Anapol said.
Open marriage differs from polygamy in that it is legal, except in those states with extremely rigid anti-adultery laws. Unlike polygamy, in an open marriage both spouses agree to allow each other to have extramarital affairs and relationships can extend to people outside of a formally bound group.
In the open marriages of the 1970s, couples would often set rigid rules about whom they would allow to engage in sex with their partners.
Couples would meet in sex clubs or private parties and swap partners. These relationships were almost always purely sexual, and temporary lovers were rarely introduced to spouses.
Contemporary practitioners of polyamory have changed the rules, and in many cases thrown them out all together, said Dossie Easton.
According to Easton, polyamory is as much a reflection of changes in '70s-style open marriages as it is a reflection of broad changes in attitudes about casual sex.
"There has been a real change in attitudes," Easton said. "We used to make a huge notion that if you picked up someone at a singles bar and didn't want to marry them in the morning you shambled out of their house."
"Nowaday, we have all kinds of open sexual connections with people that we call friends that we are not auditioning for marriage."