We document for the first time the diet of a privileged French population from Brittany, a region that was the center of battles between the Kingdoms of England and France until the end of the fifteenth century. We present here the results of stable isotope analyses of carbon, nitrogen, and sulfur of human and animal bone and tooth collagen for a late medieval to early modern Breton population. The isotopic values observed for the Dominican convent of Rennes, Brittany, are very similar to those reported for medieval archaeological populations in Great Britain, namely they have enriched δ 15 N values combined with almost entirely terrestrial carbon signals. We discuss the consumption of young animals in a diet made up of terrestrial, marine, and freshwater resources. We report dietary differences between socioeconomic groups and gender, with women and nobles (male and female) showing patterns consistent with high animal product consumption and lower mobility. The S isotope ratios of both humans and fauna are very homogeneous and generally have coastal δ 34 S values. The convent is known to have been an interregional pilgrimage site during the early modern period, but the isotope values indicate that the identified migrants were not pilgrims. Stable isotope analysis therefore complements the available historical information on human diets and mobility.