Duke of Aosta was a title in the Italian nobility. It was established in the 13th century when Frederick II, Holy Roman Emperor, made the County of Aosta a duchy. The region was part of the Savoyard state and the title was granted to various princes of the House of Savoy, second sons of the reigning king of Sardinia or king of Italy.

Amadeo I, also known as Amadeus, was an Italian prince who reigned as King of Spain from 1870 to 1873. The only king of Spain to come from the House of Savoy, he was the second son of Victor Emmanuel II of Italy and was known for most of his life as the Duke of Aosta, the usual title for a second son in the Savoyard dynasty.