Casting

As inspiration for the crowd scene in the film, the production staff spent a long time looking at the Simpsons poster that features over 320 of the show's characters. Groening said that they did try to put every single character into the film, with 94 having speaking parts. The series regulars Dan Castellaneta, Julie Kavner, Nancy Cartwright, Yeardley Smith, Hank Azaria and Harry Shearer, and semi-regular performers Marcia Wallace, Pamela Hayden and Tress MacNeille reprised their roles. Kelsey Grammer returned as Sideshow Bob, as did Joe Mantegna for Fat Tony, while Albert Brooks, who supplied many guest voices in episodes, was hired as Russ Cargill,the film's villain. The cast began recording every week from June 2006 onwards,[ with James L. Brooks directing them for the first time since the television show's early seasons. Castellaneta described the recording sessions as "much more intense" than recording the television series, with them particpating in "20 or more" sessions, and more emotionally dramatic than the TV series.

Isla Fisher will voice a character, though she couldn't say who she was voicing due to a confidentiality agreement. Among those playing themselves are Erin Brockovich, and Green Day. Nancy Cartwright said that she was not there the day Green Day recorded their part, with Yeardley Smith admitting that she did not even know the group appeared in the film until she was told by MTV. Groening called Green Day "really nice guys" and "really good sports", whilst Hank Azaria as Moe had the chance to "yell out obnoxious stuff" at them. An as-yet-unrevealed "very big star" will feature in a secret cameo role. Minnie Driver recorded the part of a patronizing grievance counselor in a scene that ended up being cut. Driver found recording her part "the funniest afternoon of her career", and was saddened when she was told it was cut, but she was not angry with Brooks or Groening. Although he does not provide the voice, Arnold Schwarzenegger is President of the United States in the film. He was chosen ahead of the incumbent President George W. Bush as "in two years that'd mean the film [would be] out of date."