The Cat o' Nine Tails (Italian: Il gatto a nove code) is a 1971 film produced in Italy, and directed by Dario Argento, adapted from a story by Dardano Sacchetti, Luigi Cozzi, and an uncredited Bryan Edgar Wallace. It stars Karl Malden, James Franciscus, and Catherine Spaak.

Although it is the middle entry in Argento's so-called "Animal Trilogy" (along with The Bird with the Crystal Plumage and Four Flies on Grey Velvet), the "cat o' nine tails" does not directly refer to a literal cat, nor to a literal multi-tailed whip; rather, it refers to the number of leads that the protagonists follow in the attempt to solve a murder.

The film was a commercial success in Italy but not in the rest of Europe. However, it was acclaimed in the United States. Argento admitted in the book Broken Mirrors, Broken Minds: The Dark Dreams of Dario Argento that he was less than pleased with the film, and has repeatedly cited it as his least favorite of all of his films.