PASSION FOR PENCILS / YOUTUBE.COM

In 2011, the British publishing house Laurence King asked Johanna Basford, a Scottish artist and commercial illustrator specializing in hand-drawn black-and-white patterns for wine labels and perfume vials, to draw a children’s coloring book. Basford suggested instead that she draw one for adults. For years, she told her publishers, her clients had loved to color in her black-and-white patterns. The publishers were convinced, and ultimately ordered an initial print run for “Secret Garden: An Inky Treasure Hunt and Coloring Book” of thirteen thousand copies. Since the book’s release, in 2013, it has sold about two million copies worldwide; for a time earlier this year, “Secret Garden” and a follow-up, “Enchanted Forest: An Inky Quest and Coloring Book,” were the two best-selling books on Amazon. “If someone saw you coloring in one of my books, they wouldn’t give you a weird look, because it’s the same kind of artwork you would see on a champagne bottle,” Basford told me. “The artwork itself is sophisticated––not like a car or a bunny with a bow in its hair.”

Coloring books for adults have been around for decades, but Basford’s success—combined with that of the French publisher Hachette Pratique’s “Art-thérapie: 100 coloriages anti-stress” (2012), which has sold more than three and a half million copies worldwide, and Dover Publishing’s “Creative Haven” line for “experienced colorists,” which launched in 2012 and sold four hundred thousand copies this May alone—has helped to create a massive new industry category. “We’ve never seen a phenomenon like it in our thirty years of publishing. We are on our fifteenth reprint of some of our titles. Just can’t keep them in print fast enough,” Lesley O’Mara, the managing director of British publishers Michael O’Mara Books, wrote to me about their own adult-coloring-books catalogue.

The trend has been fuelled to some degree by social media—colorists post their elaborate creations on Facebook and Pinterest, garnering fans and offering pro tips on things like Prismacolor versus gel pens, or how to make that tricky owl in the corner pop—and by marketing that associates them with such therapeutic ends as anxiety- and stress-reduction. But it is also part of a larger and more pervasive fashion among adults for childhood objects and experiences. This “Peter Pan market” has roots in publishing, beyond coloring books (the growth in sales of children’s and young-adult books to much older readers has been well documented), but it is far from confined to that arena.

Summer camps for adults, for example, have also gone from curiosity to viable enterprise. Following a near-death experience, Fidget Wigglesworth (birth name: Levi Felix), then the vice-president of a successful dot-com, turned off his phone and went backpacking for two and a half years with his partner, Brooke Dean; when they returned, in 2012, they founded Camp Grounded, a “Digital Detox” experience for which campers relinquish their electronic devices and engage instead in stargazing and sing-alongs. In 2013, Adam Tichauer founded Camp No Counselors, a summer camp for adults, in upstate New York; it has since expanded to Chicago, Nashville, and Los Angeles, and this year’s sessions are nearly sold out, at up to five hundred and seventy-five dollars per weekend. The camp’s “most quintessential” event, according to its F.A.Q. page, is Color War, which involves everything from tug-of-war to apple bobbing to flag design—practically every childhood activity except coloring.

Another example is Preschool Mastermind, a series of weekly preschool classes for adults in Brooklyn: participants make crafts with glitter glue, have naptime, and pose for class pictures, with sessions priced on a sliding scale from three hundred and thirty-three dollars to nine hundred and ninety-nine. “Play is different than ‘playing along,’ ” Michelle Joni Lapidos, the organizer of the sessions, wrote to me. “Play breeds physical health and mental well-being. People who didn’t play growing up become serial killers and stuff.”

While that claim is clearly too deterministic, it nods to an actual study. In 1966, Stuart Brown, a physician and psychiatrist, investigated the background of Charles Whitman, a mass murderer in Texas, and realized that the Whitman had had essentially no opportunities for play during childhood; Brown subsequently did a pilot study of twenty-six mass murderers and discovered that ninety per cent of them had lacked playtime during childhood. (But then, ninety per cent had also been physically abused.) Brown went on to found the National Institute for Play, in 2006, which argues for the benefits of playtime for people of all ages. In his book “Play: How It Shapes the Brain, Opens the Imagination, and Invigorates the Soul” (2010), he writes, for example, of “Laurel,” a C.E.O. whose “irrational bliss” during horseback riding and spontaneous play “has spilled over into her family and work.” Such anecdotes have been backed by some psychological research. Brown’s book drew on more than six thousand “play histories” that he conducted across four decades, while an article on playfulness in adults published earlier this year in the American Journal of Play cited findings that play correlates with academic and reproductive success, stress reduction, and innovative performance at work.

These kinds of studies translate into marketing claims that can go overboard, if rarely to the extent of “Play prevents murdering.” The word “therapy” appears frequently in adult-coloring-book titles, for instance, while Dover’s Creative Haven series is marketed as “an escape to a world of inspiration and artistic fulfillment.” Susan Linn, a psychologist at Harvard Medical School, pointed out to me that, however soothing and enjoyable coloring might be, these books aren’t even an especially creative endeavor for children, and that products marketed as therapeutic play sometimes barely qualify as playful. They hold users by the hand, she said, whereas “the best toys are ninety per cent child and ten per cent toy.” Coloring might help to release tension, but it’s a fundamentally more directed and restrictive activity than painting something from scratch.

Susan Jacoby, the author of “The Age of American Unreason,” was more unequivocally skeptical of the phenomenon. “There’s a line from the Bible, ‘When I was a child, I thought as a child, but as an adult, I put away childish things,’ ” she said. “The coloring book is an artifact of a broader cultural shift. And that cultural shift is a bad thing.” According to Jacoby, adults who immerse themselves in escapist fantasies like coloring books, camps, and preschool are regressing into safe patterns in order to avoid confronting the world around them. “I think the whole popularity of young-adult literature is a general decline of people not wanting to do things that require effort,” she said. She also suggested that the Great Recession might have contributed to the broader cultural shift, with people in their twenties moving back into their childhood homes because they couldn’t get jobs, and experiencing psychological retreat instead of developing as mature adults.

There is, in fact, a minor tradition in the U.S. of recessions being marketed as a time for recess activities. In 1982, during the aftermath of the nineteen-seventies energy crisis, Wham-O, maker of the hula hoop, attempted to introduce a peppermint-scented hoop into the marketplace. The original had launched in 1958, during another recession. “Wham-O has always felt that when the world is in kind of a messy way and people are unhappy, something like the hoop lets them just forget everything while they go crazy for a minute or two spinning around,” one of the company’s vice-presidents said when the scented hoop was unveiled.

The peppermint hoop failed spectacularly—history doesn’t record whether the U.S.’s emergence from the recession later that year was to blame. But with the current economic recovery coming along, if slowly, in the U.S., adult coloring books don’t seem to be experiencing the same fate. On August 2nd, Dover is inviting colorists of all ages to participate in the inaugural National Coloring Book Day. A few months later, in October, Bantam Books will release a “Game of Thrones”–themed coloring book, with George R.R. Martin himself overseeing the project. And that same month, Basford’s next book, “The Lost Ocean: An Underwater Adventure and Coloring Book,” will go on sale. “Coloring is so accessible,” she told me. “It unleashes the creativity we all have in a way that’s quite safe.”

*This post originally stated that Susan Linn is a psychiatrist; she is a psychologist.