Mixtapes, a means of sharing and listening to music that’s about as modern as the gramophone, are making a surprising comeback. It’s mostly thanks to the San Francisco Mixtape Society, a grass-roots organization that’s become an underground sensation. Since 2010, they’ve hosted semi-regular parties devoted to the lost art form of tangible playlists, which have attracted hundreds of 20-something kids, most of them born right around the time that cassettes were becoming obsolete. The rules are simple: You create a mixtape based on an ever-changing theme — past themes have included “Fools Rush In” and “Lemonade Stand” — and bring it to a Mixtape Society event to be judged by, and shared with, your peers. It’s like a Secret Santa exchange for music snobs; you bring a mixtape and leave with a mixtape. CD mixes are acceptable, but Mixtape Society co-founder John Verrochi says that “People who bring cassettes are rewarded with a free drink as an extra incentive.” The premise has taken off; mixtape parties will be launching soon in Portland, Washington D.C., Chicago, Los Angeles, New York City, Austin, and Seattle. James Brown, a 50-year-old record store employee and two-time Mixtape Society champion, thinks the mixtape renaissance has much to do with the Internet — ironically, the very technology that once helped to destroy it. “Before you had to be a diehard record collector to get access to lots of different music,” he says. “Now you can find just about anything you want for free, and it’s much easier for people to indulge their inner DJ.”

(This story originally appeared, in a slightly different form, in the November 27th, 2011 issue of the New York Times Magazine.)