Out Stack (Scots: Ootsta) is an island in Shetland, and the northernmost point of Scotland, the United Kingdom, and the British Isles.

It lies 600 m (2,000 ft) northeast of Muckle Flugga and 1+1⁄2 nautical miles (3 kilometres) north of the island of Unst.

It is one of the North Isles of the Shetland Islands and lies within the Hermaness National Nature Reserve.

Jane Franklin, the wife of the Arctic explorer John Franklin, landed on Out Stack after John Rae's reports of the fate of the Franklin expedition had reached Stromness, Orkney, where she lived, in 1853/54.

[2] The Hermaness National Nature Reserve covers the Muckle Flugga rocks and Out Stack, as well as the seabird cliffs and moorland of Hermaness.