Árainn Mhór (English name: Arranmore) is an island off the west coast of County Donegal, Ireland. Arranmore is the largest inhabited island of County Donegal, with a population of 514 in 2011, down from 528 in 2006, 543 in 2002, and over 600 in 1996. The island is part of the Donegal Gaeltacht
It is also known in English as Aran Island (not to be confused with the Aran Islands off Galway Bay or the Scottish Isle of Arran). In Irish the island was traditionally called Árainn; the adjective mór (large) was added fairly recently. It was also sometimes called in Irish Árainn Uí Dhomhnaill, meaning the 'Aran of the O'Donnells'.
There are 529 people living on Aranmore and 62% are native Irish speakers.
The island lies 5 km (3 mi) off Burtonport, a small coastal village in The Rosses, and is served by two ferry services, a conventional ferry that accommodates up to 96 foot passengers and all sizes of vehicles. This journey takes 15 minutes. In 2007, a fast ferry service commenced which can cover the run to the island in 5 minutes. Both services run daily all year. The trip to the island passes a number of small islands before crossing a stretch of open Atlantic water.