Rennes is a city in the east of Brittany in northwestern France at the confluence of the rivers Ille and Vilaine. Rennes is the prefecture of the region of Brittany, as well as the Ille-et-Vilaine department. In 2017, the urban area had a population of 357,327 inhabitants, and the larger metropolitan area had 739,974 inhabitants. The inhabitants of Rennes are called Rennais (masculine) or Rennaises (feminine) in French.

The Duchy of Brittany was a medieval feudal state that existed between approximately 939 and 1547. Its territory covered the northwestern peninsula of Europe, bordered by the Atlantic Ocean to the west, and the English Channel to the north. It was also less definitively bordered by the river Loire to the south, and Normandy, and other French provinces, to the east. The Duchy was established after the expulsion of Viking armies from the region around 939. The Duchy, in the 10th and 11th centuries, was politically unstable, with the dukes holding only limited power outside their own personal lands. The Duchy had mixed relationships with the neighbouring Duchy of Normandy, sometimes allying itself with Normandy, and at other times, such as the Breton–Norman War, entering into open conflict.