When director Jean-Pierre Melville brought a copy of the script to Alain Delon, Delon asked him what the title was. When he was told the title was Le Samourai, Delon had Melville follow him to his bedroom, where there was only a leather couch and a samurai blade hanging on the wall.
Melville worried how he was going to shoot the scene where Jef drives the stolen car right into the scrap garage. Without missing a beat, Delon drove the car down the narrow alley and into the garage in one shot.
According to Rui Nogueira (author of the book "Melville on Melville" published in 1976), the caged bird shown as Jef Costello's pet in "Le Samourai" was the only casualty of the fire that destroyed Melville's studio in 1967.