An uninhabited island, the second-largest in the St. Kilda group, Soay (Gael: Soaigh) lies to the northwest of Hirta, the main island in the group. Trimmed by cliffs, it rises steeply to 378m (1240 feet) at Cnoc Glas and extends to 98.8 ha (244 acres). With the other islands, it is owned by the National Trust for Scotland, managed by Scottish Natural Heritage as a nature reserve and is included in the St. Kilda World Heritage Site.
It is unlikely that this island ever had permanent human habitation, but it is noted for its rare breed of sheep. The most primitive sheep in Europe, the Soay sheep resemble the original domesticated animals which were first brought to Britain around 5000 BC. They persisted on the mainland until Mediaeval times but survived here due to their geographical isolation. Some of the Soay sheep were taken to neighbouring Hirta in the 1930s to ensure their survival. A Vickers Wellington aircraft crashed on the south coast of the island on 23rd February 1943, killing the crew, a loss remembered by a memorial in St. Kilda Church on Hirta.