When John D'Leo first met Dianna Agron on-set, he unknowingly asked her if she was the Make-up Girl. Agron burst out laughing and said, "I'm your sister!"
Giovanni (Robert De Niro) is invited to talk about the movie "Goodfellas" (1990) at a special screening. De Niro starred in that movie along with several supporting cast members in this movie.
When Don Luchese (Stan Carp) receives the bucket of ice in prison, he is reading the newspaper "La Repubblica". In the top right corner of the front page a picture of "LEON" can be seen, and next to it advertisement for "NIKITA". Both films made by Luc Besson: Nikita (1990) and Léon: The Professional (1994).
After beating up the plumber with a baseball bat, Robert De Niro's character quotes a line by Al Capone: "You can get further with a kind word and a gun, than you can with just a kind word." This same line is said by De Niro when he played Al Capone in The Untouchables (1987), in which he also beat an underling with a baseball bat.
The first Luc Besson film to be shot with anamorphic lenses since Léon: The Professional (1994). All of his later films had been shot with spherical lenses in Super 35, but he decided to go back to anamorphic for this film, and surprised cinematographer Thierry Arbogast when he told him so.
The Paris SG trading cards show the names Charlie Clerc and Stéphane Robuchon, members of the film's art department.
The school attended by Belle and Warren is the "lycée Jules Vallès" (i.e. Jules Vallès High School). Jules Vallès was a French journalist and writer during the nineteenth century. There is no real "lycée Jules Vallès". The school, "collège Jean Moulin in Gacé", was transformed into the school for the film.
Fred Blake/Giovanni Manzoni (Robert De Niro) says that he needs a psychiatrist. This is a nod to De Niro's roles in Analyze This (1999) and Analyze That (2002).