The history of medieval economic thought, conventionally treated as a simple prehistoric era of economic disciplines and analysis, is here retraced as a complex phenomenon, in which man's effort to understand the economic facts of his time and the logic of exchange that articulate them is also measured by its ability to read the behaviors and relationships that underlie and legitimize them. It is an effort thanks to which medieval reflection comes to construct a taxonomy of economic-commercial relations. Market, money, merchant-bankers, but also value, interest, monopolies, profit and utility: the book analyzes the fundamental questions of the economy, the supporting categories and the key words with which the spaces, means and actors of exchange are qualified. The physiognomy of this thought is reconstructed following the development of a vast textuality produced by the Fathers of the Church, by the consecrated and lay men who made Europe, from the late antiquity to civil humanism. Assuming this multiple level of observation, the volume traces a history of economic thought in the Middle Ages that offers itself to the economic discussion of those interested in understanding economic action, to the history of the categories proposed in the modern age to become the object of choice for scientific research.