This film was the result of Project Greenlight (2001), the first-time-director competition launched by Ben Affleck, Matt Damon, and Miramax, and was the subject of the HBO documentary of the same name, which aired in Winter 2002. The documentary revealed many behind-the-scenes snafus, which led to the mid-production firing of co-producer Jeff Balis.
Sean Penn was offered the role Joe O'Malley, but turned it down and did I Am Sam (2001) in which he was nominated for an Oscar. Aidan Quinn eventually played the part.
After co-producer Jeff Balis was fired, the executive producer changed his mind the next day, crediting a conversation with his wife the night before.
Emma Thompson was offered the role of Margaret O'Malley but passed. Actresses that also passed were Allison Janney, Marcia Gay Harden, Gillian Anderson, Joan Allen, Patricia Arquette, and Laurie Metcalf. Marg Helgenberger even met for the part. The role was eventually played by Bonnie Hunt.