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.
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.
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.
At the two-thirds mark of the film, there are two shots of a chair used as a nightstand at Trelkovsky's apartment where Roman Polanski used jaw-dropping perspective effects. The first one was when a thirsty Trelkovsky tries to grab a bottle of water from the chair (2D foreshortening). The second one was when Trelkovsky walks by the chair (3D forced perspective) towards the window.