Cat Ballou is a 1965 American western comedy film starring Jane Fonda and Lee Marvin, who won an Academy Award for his dual role. The story involves a woman who hires a notorious gunman to protect her father's ranch, and later to avenge his murder, only to find that the gunman is not what she expected. The supporting cast features Tom Nardini, Michael Callan, Dwayne Hickman, and Nat King Cole and Stubby Kaye, who together perform the film's theme song, and who appear throughout the film in the form of travelling minstrels or troubadours as a kind of musical Greek chorus and framing device.

The film was directed by Elliot Silverstein from a screenplay by Walter Newman and Frank Pierson adapted from the 1956 novel The Ballad of Cat Ballou by Roy Chanslor, who also wrote the novel filmed as Johnny Guitar. Chanslor's novel was a serious Western, and though it was turned into a comedy for the film, the filmmakers retained some darker elements. The film references many classic Western films, notably Shane. The film was selected by the American Film Institute as the 10th greatest Western of all time in its AFI's 10 Top 10 list in 2008.

Catherine "Cat" Ballou, a notorious outlaw, is set to be executed in the small town of Wolf City, Wyoming. Two banjo and guitar playing "Shouters", Professor Sam the Shade and the Sunrise Kid, sing the ballad of Cat Ballou and regale the audience with the tale of how she began her career of crime.

Some months prior, Catherine, then an aspiring schoolteacher, is returning home by train to Wolf City from finishing school. On the way, she unwittingly helps accused cattle rustler Clay Boone elude his captor, Sheriff Maledon, when Boone's Uncle Jed, disguised as a preacher, distracts the lawman.

Arriving home at her father Frankie Ballou's ranch, Catherine learns that the Wolf City Development Corporation is scheming to take his ranch. Frankie's sole defender is his ranch hand, educated Native American Jackson Two-Bears. Clay and Jed appear and reluctantly offer to help Catherine. She hires legendary gunfighter Kid Shelleen to help protect her father from gunslinger Tim Strawn, the tin-nosed hired killer who is threatening him.

Shelleen arrives and proves to be a drunken bum who is a crack shot only when he is inebriated. His presence proves to be useless, as Strawn abruptly kills Frankie. When the townspeople refuse to bring Strawn to justice, Catherine becomes a revenge-seeking outlaw, known as Cat Ballou. She and her gang rob a train carrying the Wolf City payroll, then take refuge in the desperado hideout "Hole-in-the-Wall". Shelleen is shocked to discover the legendary outlaw Cassidy is, now, a humble saloonkeeper in Hole-in-the-Wall.

The gang is thrown out when it is learned what they have done, due to Hole-in-the-Wall's continued existence being dependent on the sufferance of Wolf City. Strawn arrives and threatens Cat. Shelleen, motivated by his affection for Cat, works himself into shape. Dressed up in his finest gunfighter outfit, he goes into town and kills Strawn, then reveals he is Strawn's brother.

Cat poses as a prostitute and confronts Sir Harry Percival, the head of the Wolf City Development Corporation. She attempts to force him into confessing that he ordered her father's murder. A struggle ensues; Sir Harry is killed, and Cat is sentenced to be hanged. With Sir Harry dead, Wolf City's future is hopeless, and the townspeople have no mercy for Cat. As the noose is placed around her neck, Uncle Jed, again disguised as a preacher, appears and cuts the rope just as the trapdoor opens. Cat safely falls through and onto a wagon, and her gang spirits her away in a daring rescue.