Along with Repulsion (1965) and Rosemary's Baby (1968) this film is part of a loose trilogy by Roman Polanski dealing with the horrors faced by apartment and city dwellers.
Roman Polanski visited Robert Shaw at his Irish home to discuss a part, but the meeting went so poorly, that no offer was ever made.
Although Roman Polanski plays the leading role in the film, he is given no screen credit as an actor.
Sylvia Kristel was originally cast to play the part of Stella, but after one day of shooting, she was replaced by Isabelle Adjani.
Philippe Sarde (the composer) chose the glass harmonica after having seen Polanski, at the restaurant, mimicking with his finger the action of making the glass sing. There was only one person left in the world that could play this instrument, for which Mozart wrote a few pieces.