The film was based on real life gangsters Paul Carbone and François Spirito. Alain Delon found the story in a book he was reading about French gangsters from 1900 to 1970. He produced the film looking for a vehicle for him to co-star with Jean-Paul Belmondo.
It was one of the most expensive French movies ever made with financing mostly coming from Paramount Pictures.
The Borsalino Company made fedora style hats from the late 19th century to the 20th century, with its heydays during the 1920s, 1930s and 1940s, when sales went through the roof. The title of this film comes from the name of the hat company which supplied the hats worn by the characters during the movie. The Borsalino hat company helped finance the movie.
Due to copyrights the film was not released before 2009 on either VHS, Betamax or DVD. It was released on DVD on November 19th, 2009. It is rarely shown on French television (only nine broadcasts in 44 years).
According to Jacques Deray in his biography, the shooting crew received threats from the Marseilles underworld because the producers initially wished to used the true names of mobsters who really existed.