In 1935, the French historian Marc Bloch stated that, despite being an old invention, the water mill was medieval in their real expansion. His great generalization coincided with the end of antiquity and later with feudalization of European society. Since then, several authors have addressed this issue and, although recently some have suggested that it was a more gradual process and less rapid than Bloch said, we are still far from knowing in some detail how it developed. In the late thirteenth century and first half of XIV, rivers and streams of the Empordà land hundreds of water mills are documented, most of which dedicated to grinding grain. In this book, several questions about these facilities are discussed: what were the characteristics, who were the owners, how came these to its operation, and what was the oversight by the stately and municipal authorities in the activities carried out.