The Monach Islands, also known as Heisker (Scottish Gaelic: Eilean Heisgeir), are an island group west of South Uist in the Outer Hebrides of Scotland.

The islands have been uninhabited since 1948, but were inhabited by up to 100 people for centuries leading up to 1810. They were originally abandoned due to overgrazing, but were resettled in the wake of the Highland Clearances.

The main islands of Ceann Ear (once home to a nunnery), Ceann Iar and Hearnish are all linked at low tide. It is said that it was at one time possible to walk all the way to Baleshare, and on to North Uist at low tide.

The islands are known for their grey seal population, and also have a large number of nesting seabirds and a rich flora. The islands are home to a small, unstaffed light, built to replace a lighthouse which was abandoned in 1943.

Smaller islands in the group include Deasker , Shillay and Stockay .