L.B. Jeffries (Jimmy Stewart), an adventurous photographer, is temporarily immobilized by a serious leg injury. Bored, and living in a time where TV and internet were not available as distractions, he watches the courtyard out his real window and speculates about the lives of the neighbors that he sees. In particular, he wonders whether his neighbor Thorvald (Raymond Burr, who actually looks older than his later character Perry Mason) may have killed his wife.
Hitchcock examines the situation from numerous points of view. At one extreme, Jeff could be considered a brilliant detective who sleuths out a case based purely on close observation. At the other end, he could be considered a voyeur and a paranoid whose suspicions could damage other people. These interpretations are voiced by his acquaintances, including his nurse (Thelma Ritter) and his fiance (Grace Kelly, the future Princess Grace of Monaco). In the end physical evidence is found that settles the Thorvald case but leaves Jeff's motivation still in question.
Hitchcock takes advantage of the situation to introduce numerous subplots -- but they're MINIMALIST subplots, where the audience only sees what Jeff sees from his window. (Mild spoilers follow) Newlyweds quarrel, a depressed woman considers suicide but is rescued by a neighbor; a sexy girl ("Miss Torso") turns out to be not a party girl but devoted to an absent boyfriend.
An entertaining thing about this movie is that we have numerous actors -- Stewart, Kelly, and Burr -- who are to become more famous for later movies and incidents.