can be a hobby.

Brian and his wife, both in their early forties, like to meet new couples privately over dinner and drinks to talk and gauge mutual interest in trading partners for sex. “I’m very happily married,” he says.

According to Brian, the allure is mainly in the and suspense—before the sex. He likes those moments at dinner when "you don't know how the night is going to end.”

“Let's face it, it’s easy for a married couple to fall into a day-to-day rut. Work, kids, house chores, bills, repeat…,” Brian says. Swinging adds some excitement.

Online sites make it easy, and more people may be taking the plunge, says Curtis Bergstrand, a sociologist at Bellarmine University in Louisville, Kentucky, and the author of Swinging in America: Love, Sex and in the 21st Century. Swingers are "very much in love and have lots of trust," he says. "The sex is just recreation."

“I’ve never heard anyone say that swinging improved their marriage,” says Rachel Sussman, relationship expert and author of The Breakup Bible. But she’s noticed that swingers tend to begin their relationship with an “open attitude to sex” and may have started swinging early on. The key, she says, is to establish “hard and fast rules” before you start: What can each person do?

"Soft swap" couples engage in all sorts of fun except swapping partners for intercourse. “Full swap" couples go all the way. Some stipulate "same room only" play. Others are okay with seeing their partner go off into another room for some privacy. Some don't allow open-mouth kissing, which is sometimes considered more intimate than sex. Some go to public swing events, while others meet with only one other couple at a time.

Even though many people assume that swinging is a man’s , it’s often the woman who finds herself enjoying it more, Bergstrand says. Men are more likely to feel competitive with other men, wondering if their wives preferred their swinging partners, while women tend to be supportive of each other within the swinging scene, he says.

Swingers aren't the same as couples who embrace more than one relationship at a time, with any number of variations on what feelings can develop. Some poly spouses call themselves primaries and take on secondaries who may turn into close connections seen privately on a predictable routine.

Swingers instead mostly do their extra-marital playing together as a couple and make sure to keep things light and fun. Depending on whom you ask, a heterosexual open marriage could be poly or swinging or some arrangement unique to the couple.

Swingers tend to want to swing with their counterparts. “You will see all shapes, sizes, and races at events and clubs,” Brian says, “But you will usually see the 8's paired up with the 8's and the 3's with the 3's.”

Being ethical and talking about safe sex and STDs is part of the drill. Dan, a 52-year old swinger from New Jersey, has herpes and is careful to disclose the risks to new partners. Even with condoms, swingers risk picking up viruses like herpes and HPV (human papillomavirus), a precursor that can lead to cervical and throat cancers.

Do swingers have more sexual issues than non-swingers? When Bergstrand conducted an online survey in 1999, speaking with over 1000 self-identified swingers, he concluded that they didn't possess any particular history of or any other special psychological profile.