The show began as a pilot called "It's Always Sunny on TV" and was shot on a digital camcorder by Day, Howerton and McElhenney. After viewing the pilot, FX Networks executives gave them $400,000[citation needed] to shoot the first season. Although it is often stated publicly that the pilot was shot for $200, the makers of the show have claimed that the cost was much lower because the only costs were videotapes. In an interview on The Daily Show, actor Danny DeVito specified that the cost was only $85 (August 3, 2006).

According to Rob McElhenney, word of mouth on the show was good enough during the first season for FX to renew it for a second, which premiered on June 29, 2006. In the new season Danny DeVito joined the cast, playing the father of Dennis (Howerton) and Dee (Olsen).

The first season finale aired on September 13, 2005. Reruns of edited first season episodes began airing on FX's parent network, FOX, in 2006. In the UK and Ireland, Bravo broadcast the first season in early 2006, with the second season to be broadcast in November 2006 according to the Sun's TV magazine. It is also shown on Channel 6 in Ireland. The show is also shown in Sweden, and in Canada where it airs on Showcase. The first season aired in the Arab world on Showtime Arabia's Paramount Comedy Channel in November 2006. FX has ordered a third season, to premiere in September, 2007.

IT'S ALWAYS SUNNY IN PHILADELPHIA SEASON 4 TITLE LIST

Season 4, Episode 1: The Gang Gets Extreme: Home Makeover Edition

Season 4, Episode 2: Mac and Dennis: Manhunters

Season 4, Episode 3: Mac and Charlie Die

Season 4, Episode 4: Dennis Reynolds: An Erotic Life

Season 4, Episode 5: Frank Buys a Billboard

Season 4, Episode 6: Who Pooped the Bed?

Season 4, Episode 7: Episode #4.7

Season 4, Episode 8: Frank Exploits the Mortgage Crisis

Season 4, Episode 9: Episode #4.9

Season 4, Episode 10: The Gang Cracks the Liberty Bell

Season 4, Episode 11: Mac Dates the Waitress