An island in the Firth of Forth off the south coast of Fife opposite Braefoot Bay, separated from the mainland by a stretch of water known as Mortimer's Deep.
It was the home of a religious community linked with St Colm or St Columba, the 6th-century abbot of Iona. King Alexander I of Scotland was storm-bound on the island for three days in 1123 and, in recognition of the shelter given to him by the hermits, promised to establish a monastic settlement in honour of St. Columba. Though the king died before the promise could be fulfilled, his brother David I later founded a priory here for monks of the Augustinian order. This was eventually erected into an abbey in 1223.
The well-preserved abbey and ruins of the 9th-century hermits' cell attract visitors to the island which can be approached by boat from Aberdour and South Queensferry.
The island has an area of 10.5 ha (26 acres) and its permanent population was recorded as 2 in 2001, but 0 (2011).