The Soay sheep is a breed of domestic sheep descended from a population of feral sheep on the 100-hectare (250-acre) island of Soay in the St Kilda Archipelago, about 65 kilometres (40 mi) from the Western Isles of Scotland. It is one of the Northern European short-tailed sheep breeds.

A feral animal or plant is one that lives in the wild but is descended from domesticated individuals. As with an introduced species, the introduction of feral animals or plants to non-native regions may disrupt ecosystems and has, in some cases, contributed to extinction of indigenous species. The removal of feral species is a major focus of island restoration.