In this paper, I study the relation between the economic thought of Pierre-Joseph Proudhon and his claimed heir Silvio Gesell. I argue that their socialism can be described as a « Monetary Analysis Socialism »: both authors place the monetary institution at the very heart of their economic analysis and consider a profound transformation of the rules that govern that institution as a necessary preliminary to the advent of socialism. Their efforts to conceive non-capitalist monetary systems aren't, I argue, a fortuitous trait of libertarian thought : the will to think a coordination for individual action that does not involve central coordination makes the monetary system a central object for libertarian political thought, and the design of this institution a crucial political issue.