Bradley Cooper's father was ill with terminal cancer during the filming of this movie, and Cooper was accordingly relieved that the movie was shot in his hometown of Philadelphia so that he could check on his father every day.
Shia LaBeouf was cast as Eddie, but had to drop out after badly injuring his left hand in a car accident in July 2008.
In a rare move, writer Leslie Dixon sold the screenplay for the film under the condition that her script would not receive rewrites from any other screenwriter.
The apartment Eddie Morra lives in (shown in the introduction scenes, along with the final scenes) is the same apartment shown in Kick-Ass: Quebrando Tudo (2010).
Throughout production, the film was called "The Dark Fields," the same name of the book on which it was based.