Profound changes in the structures and beliefs of medieval society, particularly medieval France, took place in the 10th to 12th centuries. The majority of our sources to apprehend these changes are monastic, which is inseparable from the fact that these same centuries represent the Golden Age of Western monasticism. Cluny emerges as one of the most important monasteries, if not the most important, in the period. Therefore, it offers a marvellous avenue to understand the society of its time. The first half of the seminar is devoted to an in-depth study of the famous Burgundian abbey. It left behind the largest corpus of sources (especially customaries, lives of saints and charters). Reading these sources and the studies concerning them will give the opportunity to investigate Cluny’s daily life, ideal of reform, and relationships with the exterior world. The second half of the seminar enlarges on this last topic: interactions between the monks and the laity, between traditional and new monasticism, as well as between the monks and the secular Church is explored.