Castel del Monte (Italian for "Castle of the Mountain"; Barese: Castìdde du Monte) is a 13th-century citadel and castle situated on a hill in Andria in the Apulia region of southeast Italy. It was built during the 1240s by King Frederick II, who had inherited the lands from his mother Constance of Sicily. In the 18th century, the castle's interior marbles and remaining furnishings were removed. It has neither a moat nor a drawbridge and some considered it never to have been intended as a defensive fortress. However, archaeological work has suggested that it originally had a curtain wall.

The castle is famous for its bold octagonal plan, and classicizing details of the architecture. In 1996, Castel del Monte was named a World Heritage Site by UNESCO, which described it as "a unique masterpiece of medieval military architecture". Described by the Enciclopedia Italiana as "the most fascinating castle built by Frederick II", it also appears on the Italian version of the one cent Euro coin.