Production

The production staff of The Simpsons had entertained the thought of a film since early in the series, but things never came together. Groening felt a feature length film would allow them to increase the show's scale and animate sequences too complex for a TV series. The season 4 episode "Kamp Krusty" was originally going to be a film, but difficulties were encountered in writing a feature length script, at which point the plans were dropped in favor of a season premiere.For a long time the project was held up. There was trouble finding a story that was right for a film, and the crew did not have enough time to complete such a project, as they already worked full time year-round on the show.Groening also expressed a wish to make Simpstasia, a parody of Fantasia, although it was never produced, partly because it would have been too difficult to write a feature-length script.Before his death, Phil Hartman had wished to make a live action Troy McClure film, and several of the show's staff had expressed a desire to help create it.

The voice cast was finally signed on to do the film in 2001, and work then began on the script. Groening and Brooks invited back Mike Scully and Al Jean (who continued to work as showrunner on the television series) to produce the film with them. They then signed David Silverman, who in anticipation of the project had quit his job at Pixar, to direct. The "strongest possible" writing team was assembled, with many of the writers from the show's early seasons being chosen for the film.David Mirkin, Mike Reiss, George Meyer, John Swartzwelder and Jon Vitti were selected. Ian Maxtone-Graham and Matt Selman joined later, and Brooks, Groening, Scully, and Jean also wrote parts of the script.Sam Simon did not return having left the show over creative differences in 1993, nor did Conan O'Brien, who wanted to work with the Simpsons staff again. O'Brien joked, "Truth be told, I worry that the Simpsons-writing portion of my brain has been destroyed after 14 years of talking to Lindsay Lohan and that guy from One Tree Hill, so maybe it's all for the best."The same went for Brad Bird who "entertained fantasies of asking if [he] could work on the movie," but did not have enough time because of work on Ratatouille.The producers arranged a deal with Fox that meant they could abandon production at any point if "they weren't satisfied with the results."

Work continued on the screenplay from 2003 onwards and did not cease,taking place in the small bungalow where Matt Groening first pitched The Simpsons in 1987. The writers spent six months discussing a plot, and each pitched a "half-assed" idea. Al Jean suggested the family rescue manatees, which became the 2005 episode "Bonfire of the Manatees", and there was The Truman Show-esque notion of the characters discovering their lives were a TV show, which Groening rejected as he felt "that the Simpsons never become aware of themselves as celebrities." Groening read about a town that had to get rid of pig feces in their water supply, which inspired the plot of the film. The decision to have Flanders in an important role also came very early on, as Jean wished to see Bart wonder what his life would be like if Flanders were his father. Having eventually decided on the basic outline for the film, the writers then separated it into seven sections. Jean, Scully, Reiss, Swartzwelder, Vitti, Mirkin, and Meyer wrote twenty five pages each, with the group meeting one month later to merge the seven sections in to one "very rough draft." The writers wrote the script in a way that they almost always employed when writing the television series, sitting around a table and pitching ideas, trying to make each other laugh.The script went through one hundred revisions. Groening described his desire to also make the film dramatically stronger than a TV episode, as "we wanna really give you something that you haven't seen before. There are moments you actually forget that you're watching a cartoon and that is difficult when you have characters as ugly as the Simpsons."

The film was originally planned for release in summer 2006,but Al Jean stated at San Diego's Comic-Con International 2004 that the producers were taking their time, to make sure that the film was perfect.In 2005, Nancy Cartwright told BBC Radio 1 that the cast had done their first table reading,and two more followed.Groening also intended the film to be made after the show ended, "but that intention was undone by good ratings."The producers were initially worried that creating a film would have negative effects on the series, as they did not have enough manpower to focus their attention on both projects. As the series progressed, more writers and animators were hired so that both the show and the film could be produced at the same time.Twentieth Century Fox finally confirmed on April 1, 2006 that The Simpsons Movie would be produced for a worldwide release date on July 27, 2007.To prevent the leaking of spoilers the film's plot was kept a secret,with the script kept under lock-and-key.In tribute to Return of the Jedi's codename "Blue Harvest", the film was dubbed "Yellow Harvest", which was the name that the film was registered under in the United States Copyright Database. Little information on the plot was released in weeks building up to the film's release. Groening noted, "I can't imagine people look in the TV section of the newspaper and think, 'I'll watch this week's Simpsons because I like the plot.' You just tune in and see what happens."