Trivia: While the time period of the movie isn't explicitly stated, the movies showing at the cinema the Waynes are at (Zorro The Gay Blade, Wolfen, Excalibur, and Arthur) were all released in 1981, making that the likely year it's set. The Zorro reference is certainly a nod to established comic continuity, where the Waynes were watching The Mark Of Zorro.
Trivia: Director Todd Phillips has specifically said that he doesn't see this movie connecting with any other DC movies - it stands alone.
Trivia: Arthur and Sophie go to a diner on Jerome Avenue. The Gotham TV series featured twin brothers, Jerome and Jeremiah, the latter of which ended up becoming the Joker in the series.
Trivia: Joaquin Phoenix won the Oscar for Best Actor for his role in this film. This marked the second time an actor won an Oscar for playing a character that was played previously by another actor that also won an Oscar for their role. The other time was Phoenix's costar in this film, Robert De Niro, winning Best Supporting Actor for playing the younger version of Vito Corleone in "The Godfather Part II," following Marlon Brando winning Best Actor for the first film.
Trivia: The use of "Rock and Roll Part 2" by Gary Glitter within this film caused controversy shortly after the film's release due to the perceived possibility that Glitter, a convicted sex offender, might collect royalties from the song's use in the film. This concern was unfounded, though, since Glitter had long since sold the rights to the song's use; the US rights are currently held by the Universal Music Publishing Group.