Synopsis

Four egocentric friends run a neighborhood Irish pub in Philadelphia and try to find their way through the adult world of work and relationships. Unfortunately, their warped views and precarious judgments often lead them to trouble, creating a myriad of uncomfortable situations that usually only get worse before they get better.

thumb|alt=A dilapidated brick building, the filming location of It's Always Sunny In Philadelphia|right|Exterior shots of Paddy's Pub are shot at the Starkman Building on 544 Mateo Street in Los Angeles.

After viewing the pilot, FX Network ordered the first season.

"The network came to us and said, 'We don't want a show about actors,' and we said, 'Fine, let's put it somewhere else, Mac explained.

"I'm from Philly, let's put it in Philly, and we'll make it about a bar, because that's a job where you can have lots of free time and still have income that could explain how these people can sustain themselves." The title was later changed to reflect that, in the unaired pilot, the gang had been rewritten as bar owners in Philadelphia, instead of actors in LA.

Prior to Kaitlin Olson joining the show, the character Sweet Dee was going to be played by Jordan Reid, who at the time was the girlfriend of Mac.

After the first season, FX executives were worried about the show's low ratings and demanded that changes be made to the cast.