Oskar Werner was cast because François Truffaut wanted someone who spoke French with a slow delivery.
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.
Jeanne Moreau had to jump into a river because her stunt double turned up drunk. Moreau then had to spend 2 days ill in bed.
Jeanne Moreau kept a lot of her wardrobe.
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.
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.
François Truffaut hated filming love scenes, which is why Jim and Catherine's big scene is shot in half darkness.
François Truffaut wanted to make a film with Jeanne Moreau as far back as 1957. He told her this when he bumped into her at Cannes at a screening of Ascenseur pour l'échafaud.
François Truffaut was greatly saddened when Henri-Pierre Roché died before he could see how Truffaut filmed his novel.
François Truffaut's script also drew on material from the diaries that Henri-Pierre Roché kept for nearly 60 years.
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.
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.
In Jean-Luc Godard's picture Une femme est une femme, Jeanne Moreau appears as herself. This becomes obvious because Jean-Paul Belmondo's character, while meeting her at a café, asks her: "How is 'Jules And Jim' coming?" Une femme est une femme was released in 1961, while Jules et Jim in 1962, but the reference exists because François Truffaut and Godard were friends at the time, and often collaborated in each other's movies.
Made with a crew of only 15.
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.
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.
When the production ran out of money, Jeanne Moreau bailed it out with her own personal financial contribution.