The Zanzibar red colobus is a species of red colobus monkey endemic to Unguja, the main island of the Zanzibar Archipelago, off the coast of Tanzania. It is also known as Kirk's red colobus after Sir John Kirk, the British Resident of Zanzibar who first brought it to the attention of zoological science. It is now classified as an endangered species and in the mid-1990s was adopted as the flagship species for conservation in Zanzibar. The population is still decreasing, and conservationists are attempting to work with the local government to devise a proper, effective strategy to protect the population and habitat. Challenges include the species' habitat, which is limited to the archipelago. The species has been reclassified three times; it was previously in the genus Colobus, then in the genus Procolobus, and later in the genus Piliocolobus.

Red colobuses are Old World monkeys of the genus Piliocolobus. It was formerly considered a subgenus within the genus Procolobus, which is now restricted to the olive colobus. They are closely related to the black-and-white colobus monkeys, and some species are often found in groups with the blue monkey. The western red colobus is frequently hunted by the common chimpanzee.