Here's some background and inside jokes to help fill in some of the gaps for viewers who don't watch both Philly-based shows.

The outrageous Abbott Elementary and It’s Always Sunny In Philadelphia crossover proved that the best combinations are ...

The Abbott Elementary & It's Always Sunny In Philadelphia crossover had hilarious character interactions, but it hid callbacks in its witty writing.

The star of the FX series also admits he was initially hesitant about the crossover concept as 'It's Always Sunny in ...

Two comedy forces collided this week on Abbott Elementary, as the school staff welcomed the Paddy’s Pub gang from FXX’s It’s Always Sunny in Philadelphia ... She calls the lawyer for that incoming ...

There's something about FXX's Rob McElhenney, Charlie Day, Glenn Howerton, Kaitlin Olson, and Danny DeVito-starring It's Always Sunny in Philadelphia that's bothered me over the past few years.

The cast of "It's Always Sunny in Philadelphia" will appeared on "Abbott Elementary." Here's how to watch, when it airs and what to know about the crossover.