The Manx cat (ˈmæŋks, in earlier times often spelled Manks) is a breed of domestic cat (Felis catus) originating on the Isle of Man, with a naturally occurring mutation that shortens the tail. Many Manx have a small stub of a tail, but Manx cats are best known as being entirely tailless; this is the most distinguishing characteristic of the breed, along with elongated hind legs and a rounded head. Manx cats come in all coat colours and patterns, though all-white specimens are rare, and the coat range of the original stock was more limited. Long-haired variants are sometimes considered a separate breed, the Cymric.
Manx are prized as skilled hunters, and thus have often been sought by farmers with rodent problems, and been a preferred ship's cat breed. They are said to be social, tame and active. An old local term for the cats on their home island is stubbin or rumpy. Manx have been exhibited in cat shows since the 1800s, with the first known breed standard published in 1903.
Tailless cats, then called stubbin (apparently both singular and plural) in colloquial Manx language, were known by the early 19th century as cats from the Isle of Man, hence the name, where they remain a substantial but declining percentage of the local cat population. The taillessness arose as a natural mutation on the island, though folklore persists that tailless domestic cats were brought there by sea. They are descended from mainland stock of obscure origin. Like all house cats, including nearby British and Irish populations, they are ultimately descended from the African wildcat (Felis lybica) and not from native European wildcats (Felis silvestris), of which the island has long been devoid.
The dominant trait of taillessness arises from a spontaneous mutation, the Manx taillessness gene, that eventually became common on the island because of the limited genetic diversity of island biogeography (an example of the founder effect and, at , of the species-area curve).
In the Manx language, the modern name of the breed is kayt Manninagh, literally 'cat of Mann' (plural kiyt or kit), or kayt cuttagh lit.