Abstract: We often imagine that money is a simple stand-in for value. In fact, money has an internal design; it is collectively engineered by the societies that use it. Decoding money’s design reveals that money holds value based on its use for public obligations and the premium it carries in private exchange. Decoding money’s design also exposes moments of radical change in its collective engineering. Christine Desan compares the design of commodity money with the design of money produced by modern banks of issue. The modern method shares the monopoly traditionally held by the public with private actors, pays them for money creation, and institutionalises self-interest at the heart of the political economy.