Josselin Castle (French: Château de Josselin, Breton: Kastell Josilin, Latin: Castellum Joscelini) is a medieval castle at Josselin, in the Morbihan department of Brittany, France, first built in 1008 by Guéthénoc, viscount of Porhoët. The town and castle were named after Guéthénoc's son, Goscelinus, and rebuilt at various times since. The current castle was built by Olivier de Clisson after 1370. He had acquired the land as part of the dowry on his marriage to Margaret of Rohan. It has been designated as a monument historique since 1928.