Book section: Trying to understand what goods are worth of is at the very heart of economists’ thinking. The answer traditionally given to this question consists in identifying a certain substance, labor, or utility, as being at its origin. The approach of the economics and sociology of conventions takes a completely different path: value is a sui generis social construct, based on monetary convention. This represents a decisive break with traditional economic approaches. Money institutes value. The power invested in money stems from its collective recognition as a purchasing power. In this sense, like language, money is a community fact; it exists only in the context of its community of use, from which it derives its power. In so doing, the proposed construction is reminiscent of Boltanski and Thévenot’s polity model: money must be seen as the “higher common principle” through which everyone is brought into relationship with others. The desire for money, rather than the search for useful commodities, is the elementary force at the heart of the functioning of commodity production. From this perspective, money can be described as “sovereign”, and the monetary community can be compared to the political community. In both cases, one can see a set of originally separate individuals building, through their association, a collective body that transcends and protects them. The monetary institution, like the state, has the nature of a collective power that the association gives itself when it constitutes itself as a social body.