The Mormaer or Earl of Buchan was originally the provincial ruler of the medieval province of Buchan. Buchan was the first Mormaerdom in the High Medieval Kingdom of the Scots to pass into the hands of a non-Scottish family in the male line. The earldom had three lines in its history, not counting passings from female heirs to sons. Today, it is held by the Erskine family as a peerage. The current holder is Harry Erskine, 18th Earl of Buchan.

Buchan is a coastal district in the north-east of Scotland, bounded by the Ythan and Deveron rivers. It was one of the original provinces of the Kingdom of Alba. It is now one of the six committee areas of Aberdeenshire.