This article studies the role copper coinage, mainly of Chinese origin, played as the currency of preference in medieval Japan and the process by which it replaced commodities as the main medium of exchange. By the late fifteenth century a major watershed in the development of a money economy had been reached, when distinctions began to be made between good-quality coins and others. The practice of shroffing then became widespread. Though both the Bakufu and local magnates attempted to forbid the practice, local needs dictated which coins were circulated. A contrast in usage grew up between “pure coins” (seisen), that is authentic or standard coins, and “inferior coins,” such as those privately minted in Japan and certain Ming coins. Attention is drawn to the need to distinguish between the monetary policy and their financial policy in the anti-shroffing decrees issued by the authorities.