William Ætheling (Middle English: [ˈwiliəm ˈaðəliŋɡ], Old English: [ˈæðeliŋɡ]; 5 August 1103 – 25 November 1120), commonly called Adelin was the son of Henry I of England by his wife Matilda of Scotland, and was thus heir apparent to the English throne. His early death without issue caused a succession crisis, known in English history as the Anarchy.

Ætheling was an Old English term (æþeling) used in Anglo-Saxon England to designate princes of the royal dynasty who were eligible for the kingship.