Television crossover events, like this week’s buzzed-about meeting between Grey’s Anatomy and Private Practice, are by nature complicated. Sending the characters of a lesser-known series into a more established hit (or vice versa) is a time-honored move for studios, but making the grammar of two shows mesh isn’t always easy. Take the notorious episode of The Simpsons that crossed over with The Critic, a FOX-arranged partnership that Simpsons creator Matt Groening considered enough of an imposition on his creation that he removed his name from the credits in protest. But at their best, TV crossovers encapsulate that marvelous feeling you get when two pieces of pop culture wink at each other from across the room. When they’re done well, crossover episodes are tiny links in the sprawling fictional universe of television, from Kramer’s turn on Mad About You to Detective Munch’s appearance on Arrested Development. We count down ten great crossover television episodes, after the jump.

Cheers meets St. Elsewhere

Medical drama St. Elsewhere wasn’t shy about crossing over with other shows. In its six-season run, St. Elsewhere met in some form or another with Chicago Hope, M*A*S*H, and The Bob Newhart Show, among others. But its best mash-up occurred when the staff of St. Elgius stopped by Boston’s most famous sitcom bar for a drink. Turns out that Norm is Dr. Auschlander’s former accountant and Carla gave birth to her last child in the St. Elsewhere hospital and thinks of it as a “butchery.” It’s a bizarre bit of cross-promotion, but the interactions between Norm, Carla, and the St. Elsewhere staff do justice to both shows, keeping the cantankerous-but-lovable spirit of Cheers without losing the tension that fueled St. Elsewhere. It’s a neat trick, and one that works in no small part thanks to the writers, who make parts of the episode feel like a one-act play.