Jen Day and her boyfriend of 11 years, Pepper Mint (yes, that’s his real name), live together with their cat in a whitewashed house on a narrow, leafy street in Berkeley, Calif. They kiss and nuzzle and have date nights, like any other couple.

Just not always with each other.

Day has another boyfriend. Mint has another girlfriend — and just began seeing two other women, too. The couple practice polyamory: They have multiple committed relationships at once, with the knowledge and consent of everyone involved.

There’s a shaken belief [leading to] more openness to seeing what works rather than believing in some tradition.

Yes, it’s Berkeley, but also? Apparently more people across the country are getting on the big-love bus. Large-scale studies tracking the number of polyamorous (aka “poly”) individuals don’t exist, but evidence from polyamory groups, relationship therapists and dating websites suggests that figure is rising fast. University of Michigan psychologist Terri Conley, for instance, estimates that 5 percent of Americans are involved in consensual non-monogamous relationships.

Why are we embracing more than one partner? Skepticism of monogamy plays a part. Roughly 20 percent of U.S. marriages end in divorce. “There’s a shaken belief” leading to “more openness to seeing what works rather than believing in some tradition,” said San Francisco clinical psychologist Deborah Anapol, before she passed away earlier this year. And, in general, people have grown more open to alternative lifestyles. Of course, it’s also possible that interest in polyamory has remained stable — but people just have more opportunity to take part. Thanks, Internet!

Still, the poly-curious should think hard before making the leap. Polyamory might sound like free love, but that doesn’t mean it’s easy. Maintaining multiple healthy relationships takes McKinseyian time-management skills and grace dealing with jealousy. Skeptics worry about the welfare of children in polyamorous families. The stigma hasn’t quite worn off, either.

They don’t really think of you as a partner, but as a human.

“A lot of people get into this relationship style and don’t really have the tools to do it ethically, so people get hurt,” says Michael (last name not given), who organizes polyamory events in the San Francisco Peninsula and South Bay Area, Calif. “People are like, ‘I dated this guy who was poly and was a sleazebag.’ It gives the lifestyle a bad name.”

Polyamory has existed in most cultures, but the term “polyamory” didn’t emerge until the 1990s in San Francisco (natch), where group marriages and open relationships from the free love and queer movements coalesced into the modern polyamory movement. Since then, polyamory has taken on a variety of forms. “If you ask one person what their definition of polyamory is, it will be totally different from somebody else’s,” says Maryland-based sex and kink educator Cassie Fuller.

To wit: Fuller and her husband practice polyfidelity, in which all members are considered equal partners who remain faithful to one another. Mint and Day form intimate networks, labeling their lovers as “primary,” “secondary” and “tertiary” depending on the level of commitment. Michael and Yi-Ling (last name not given) practice relationship anarchy, participating in open relationships without ranking partners.

In relationship anarchy, “you don’t refer to your partners as partners or lovers or cuddle buddies or dating,” Yi-Ling says. “All this terminology is thrown out the window…. There are no expectations…. They don’t really think of you as a partner, but as a human.”

Sexual jealousy and possessiveness can be a problem, poly people admit. Brutally honest conversation — including about how far a partner can go sexually with someone else — can help, as can limiting talk about other partners. Sometimes jealousy can be channeled into something pretty hot.

Time-management is trickier. “That’s the real hard part — finding time to give everyone what they need,” Day says. Mint stays organized with a calendar on his cellphone, filled with rows of color-coded time slots. He and Day have a date about twice a week, and cleaning and cooking count. Day also has a weekly standing date with her other boyfriend.

It’s hard to know exactly how many people identify as polyamorous, because few universities fund research on sexual minorities. There’s not a standard definition of polyamory, either. Most poly people agree on it in principle, but fill in the details themselves. “What about a couple who thinks of themselves as swingers, but swings with the same friends for years and years, falling in love with each other?” says relationship consultant Elisabeth Sheff.

And yet, anecdotal evidence strongly suggests an upswing. Local poly organizations have experienced a surge in membership, while sex and relationship therapists have noticed a rise in poly clients. “All signs point to an upward trend,” says Niko Antallfy, a sociology lecturer at Macquarie University.

The real trend is toward more tolerance and acceptance of diversity.

Oh but the critics! There are many. Some, predictably, consider polyamory amoral. Others blame a shift toward a “me-me” culture. “We have been taught in this generation that we can have it all”— including more than one relationship, says Karen Ruskin, a Boston therapist. And polyamory remains stigmatized. “Coming out” could mean risking friendships, or more. Mint recalls one community member who lost his teaching job.

Advocates and skeptics alike agree that although polyamory will likely continue to spread, it won’t replace monogamy, because cultural and religious beliefs that condemn polyamory will continue to exist. In other words, the U.S. isn’t legalizing polyamorous marriage anytime soon. Assuming it does, sorting out the legal aspects will be a headache, from taxes to inheritance to, yes, divorce.

Yet Anapol had said “it’s only a matter of time” before the law embraces many-member marriages. Meanwhile, she predicted, more people will experiment with polyamory at some point. “The real trend is toward more tolerance and acceptance of diversity,” Anapol said.

Three needn’t always be a crowd.

Editor’s note: The story has been updated with the current U.S. divorce rate.

Video by Tom Gorman. Tom is an OZY video producer.