Finlaggan Castle is a ruined fortified house located on the isle of Eilean Mór on Loch Finlaggan, Islay, Scotland. It was once a residence and stronghold of Lord of the Isles and Clan MacDonald. Built in the 13th century, with masonry walls, possibly built on the remains of an earlier Iron Age fort. The Lords of the Isles used the castle a principal court. Iain Mor MacDonald, 3rd of Dunnyveg and his son Iain Cathanach MacDonald were taken prisoner at Finlaggan Castle, through the deception of Macian of Ardnamurchan for the hanging and execution of the governor of Dunaverty Castle and were later tried and hung on the Burgh Muir, Edinburgh. In 1541 Finlaggan was held from the Crown by Donald MacGilleasbuig. The castle appears to have been demolished in the 15th-16th century.