Dunstaffnage Castle (Scottish Gaelic: Caisteal Dhùn Stadhainis) is a partially ruined castle in Argyll and Bute, western Scotland. It lies 3 miles (5 km) NNE of Oban, situated on a platform of conglomerate rock on a promontory at the south-west of the entrance to Loch Etive, and is surrounded on three sides by the sea. The castle and the nearby chapel ruin have been a Historic Scotland property since 1958. Both are Scheduled Ancient Monuments.

The castle dates back to the 13th century, making it one of Scotland's oldest stone castles, in a local group which includes Castle Sween and Castle Tioram. Guarding a strategic location, it was built by the MacDougall lords of Lorn, and has been held since the 15th century by the Clan Campbell. To this day there is a hereditary Captain of Dunstaffnage, although they no longer reside at the castle. Dunstaffnage is maintained by Historic Environment Scotland, and is open to the public, although the 16th-century gatehouse is retained as the private property of the Captain. The prefix dun in the name means "fort" in Gaelic, while the rest of the name derives from Norse stafr-nis, "headland of the staff".