Abstract For several hundred years European armies staffed their officer corps through a system of purchase. Different ranks had different prices, and as officers moved through the ranks they would sell one commission in order to purchase the next. This basic observation, along with the large sums paid, seem incongruous with twentieth‐century views on military organization. This article argues that the system was efficient in that it solved a selection problem and provided appropriate incentives. It is argued that the internal structure, methods of payment, differences across countries and military branches, and the final collapse of the system are all consistent with this hypothesis.