Phillips and Silver wrote Joker throughout 2017 and the writing process took about a year. According to producer Emma Tillinger Koskoff, it took some time to get approval for the script from Warner Bros., partly because of concerns over the content. Similarly, Phillips commented that there were "a zillion hurdles" during the year-long writing process due to the visibility of the character. Phillips said that while the script's themes may reflect modern society, the film was not intended to be political. He also noted that Joker is a story about child trauma and mental illness. In their script, Phillips talked about how difficult it is for patients to reveal their diagnoses, referring to a line from the film: "The worst part of having a mental illness is that people expect you to behave as if you don't".
