When Jim first visits Jules' home in Austria, Catherine shows him a picture of Jules costumed as Mozart. Oskar Werner, the actor who plays Jules, also portrayed Mozart in an earlier film.
François Truffaut came across the original novel by Henri-Pierre Roché in the mid-50s whilst browsing through some secondhand books in Paris. He later befriended the author.
Director of photography Raoul Coutard used lightweight photographic equipment that hadn't been used before to create a fluid style to the camerawork, even mounting some of the cameras on bicycles.
Henri-Pierre Roché's original novel was based on his own experiences as a young man. The original Catherine was still alive when the film was released and even attended the premiere incognito.
Henri Serre was an unknown actor performing comedy in a club when he was cast as Jim. He was cast because of his physical resemblance to Henri-Pierre Roché.
Jean Renoir was a particular fan of the film and wrote a letter to François Truffaut expressing his pleasure. Truffaut carried that letter with him for years afterward.
One of the earliest foreign films to be distributed in the US by two Harvard students, Cyrus Harvey and Brian Halliday, under their newly formed company, Janus Films. Janus went on to distribute all sorts of classic foreign films and is now owned by Criterion.
The production was so small and had so little money that Jeanne Moreau was often called upon to lend her Rolls Royce for ferrying around props. She even did some of the catering, particularly in the scenes where Jim visits Jules and Catherine in Germany.