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Reciprocity, gift, and counter-gift are concepts that have been widely used by medievalists over the past decades. This paper analyzes the social relations of a Cistercian monastery in Galicia through its exchanges with the peasant communities in its hinterland and dominant local groups during the 12th and 13th centuries. It argues that reciprocity can be a valid means of analysis if we seek to explain how new social positions are defined, hierarchies are established, and social mobility and differentiation arise when power systems are organized.