When Mel Cassidy first became curious about nonmonogamy, there weren’t many helpful resources. Most of the books focused on the transition from monogamy to nonmonogamy, but Cassidy, who goes by them/them pronouns, was “freshly divorced, hadn’t really dated as an adult.”

“I was winging it,” said Cassidy, who has since become a relationship coach who specializes in consensual nonmonogamy.

Recently, however, there has been an explosion of literature on the topic, including books about polyamory and other types of open relationships. And more people are interested, too: A 2023 Pew Research survey found that 51 percent of adults under 30 considered open marriages “acceptable,” and a 2016 study of single adults in the United States has shown that more than 20 percent have experimented with some form of consensual nonmonogamy.

But even as these relationship styles become more common, there are lots of details to figure out. Partners have to decide on the approach that works best for them. There are also sexual and emotional concerns to parse when bringing new partners into the mix, said Shadeen Francis, a sex and relationship therapist based in Philadelphia.

Good books can help nonmonogamous partners “develop compassion or positive empathy for one another,” said Marie Thouin, a dating and relationship coach and researcher based in the San Francisco Bay Area. They can remind you that “you’re not alone in your choice,” she added.

We spoke to more than a dozen relationship experts and researchers for their book recommendations — whether you’re in a nonmonogamous relationship or interested in exploring.