Châteaubriant (French: [ʃɑtobʁijɑ̃] ^ⓘ; Breton: Kastell-Briant; Gallo: Châtiaoberiant) is a town in western France, about 350 km (220 mi) southwest of Paris, and one of the three sous-préfectures of the Loire-Atlantique department. Châteaubriant is also situated in the historical and cultural region of Brittany, and it is the capital of the Pays de la Mée.

A part of the traditional province of Brittany, Châteaubriant also lies on the threshold of Anjou, and it was an important stronghold in northwestern France during the Middle Ages. The town appeared during the 11th century, around a castle and a priory. A fair, which still exists, was also founded in 1050. Châteaubriant played a certain role during the Mad War between France and Brittany and became a significant cultural centre in the 16th century, when the Renaissance château was built in the medieval fortress.

The town is situated between Nantes and Rennes, and tends to be economically oriented towards the latter. The medieval fair and cattle market are still important for the local economy, but Châteaubriant also developed a metallurgical industry during the 19th century, and then plastics manufacturing during the 20th century.

Châteaubriant is noteworthy for the Château de Châteaubriant, which combines a large medieval castle and a Renaissance palace. The town also has an 11th-century church and a medieval town centre, with half-timbered houses and remains of city walls. During the Second World War, Châteaubriant had a concentration camp, and it is known in France for the 27 hostages who were shot there in 1941.

Châteaubriant lies at the north of the Loire-Atlantique département, in the middle of a triangle between Nantes, Angers and Rennes. The town is not situated on any of the roads that link the three cities, thus, it is somewhat isolated. The closest highway, linking Rennes to Nantes, is 30 km (19 mi) away.

Châteaubriant 49 km (30 mi) north of Ancenis, 68 km (42 mi) south of Rennes, 69 km (43 mi) north of Nantes, and 85 km (53 mi) west of Angers. The neighboring communes are Rougé, Saint-Aubin-des-Châteaux, Louisfert, Erbray, and Soudan.

According to the French statistical office, Châteaubriant is an urban commune, the only one in its urban unit. The metropolitan area, much wider, is made up of Châteaubriant plus several surrounding rural communes.

The commune of Châteaubriant itself encompasses not only the town, but also agricultural land and some hamlets. The main agricultural activities are forage and cereal growing, and cattle breeding (especially for beef and dairy production).