The former Breton and French Catholic Diocese of Saint-Malo existed from at least the seventh century until the French Revolution. Its see was at Aleth, to a point in the twelfth century, when it moved to Saint-Malo. Its territory extended over some of the modern departments of Ille-et-Vilaine, Côtes-d'Armor and Morbihan. Until the 860s it was often termed bishopric of Poutrocoet.
Coordinates: 48°39′N 2°02′W / 48.65°N 2.03°W