Graemsay (/ˈɡreɪmziː/) is an island in the western approaches to Scapa Flow, in the Orkney Islands of Scotland. The island has two lighthouses. Graemsay lies within the parish of Stromness.

Graemsay lies between Hoy and Stromness on Mainland Orkney, separated from the Mainland by Clestrain Sound. The island is 409 ha (1.58 sq mi) in area and is mainly crofted.

The island's geology is Old Red Sandstone of the Devonian period, with two volcanic faults. On the north coast there is granite-schist, a great rarity in Orkney.

Graemsay is surrounded by strong tidal races, known locally as roosts. An Orkney Ferries service, usually operated by MV Graemsay, links the island with Stromness and Moaness on Hoy.

Graemsay is sometimes referred to locally, as 'Orkney's green isle' due to its lush green vegetation cover.

Birds include oystercatchers, ringed plovers, redshank and curlew. Parts of the island are largely undeveloped and are a haven for wild plants.^{[citation needed]}

As with many other Orkney Islands, there is a connection to the Celtic Church, possibly a pre-Norse one. There are the remains of two early churches, dedicated to St Bride and to St Columba., who are both saints of Irish origin.

The island has two lighthouses, Hoy High (NE) and Hoy Low (NW), both built in 1851 by Alan Stevenson for the 19th-century herring industry.