Joker: Folie à Deux is a 2024 American jukebox musical legal drama film directed by Todd Phillips from a screenplay he co-wrote with Scott Silver. Based on DC Comics characters, it is the sequel to Joker (2019) and stars Joaquin Phoenix reprising his role as Arthur Fleck / Joker, alongside Lady Gaga as Harley "Lee" Quinzel. The supporting cast includes Brendan Gleeson, Catherine Keener, Zazie Beetz, Steve Coogan, Harry Lawtey, and Leigh Gill. In the film, Arthur awaits trial for his crimes at Arkham State Hospital where he develops a romantic relationship with another inmate, Lee, who is obsessed with his Joker persona.

Although Joker was initially conceived as a standalone film, its success at the box-office sparked interest in a sequel, which was announced in June 2022 with Gaga and Beetz joining later that year. Principal photography took place in New York City, Los Angeles, and Belleville, New Jersey from December 2022 to April 2023.

Joker: Folie à Deux premiered at the 81st Venice International Film Festival on September 4, 2024, and was released in the United States on October 4. The film was poorly received by critics, who deemed it inferior to its predecessor, and was a commercial failure, grossing $207.5 million worldwide on a $190–200 million budget.