At the end of the Middle Ages, Europe went through great économie and démographie upheavals. What were their sources ? What did they signify ? The responsibility for thèse events has been attributed diversely to wars, épidémies, priée fluctuations or climatic changes. This book tries to go further in the search into the origins of such a long-lasting and massive décline. Eastern Normandy, a privileged field for research because of the wealth of extant sources, has allowed the full play of quantitative analysis at two levels : macro-analysis for the major indicators (population, production, priées, wages, productivity) ; micro-analysis for the study of économie actors (peasants and lords). The confrontation of the two sets of data shows the breakdown of the socio-economic system as early as the end of the 13th century. The book thus illuminâtes the crisis of feudalism and the problem of the transition to capitalism.