This article uses Foucault’s lecture courses to illuminate his reading of Marx’s Capital in Discipline and Punish. Foucault finds in Marx’s account of cooperation a precedent for his own approach to power. In turn, Foucault helps us rethink the concepts of productive force and labour power in Marx. Foucault is shown to be particularly interested in one of Marx’s major themes in Capital, parts III–IV: the subsumption of labour under capital. In Discipline and Punish and The Punitive Society, Foucault offers a genealogy of the forms of labour power and productive force. One of his central problems is to understand how labour power is converted in productive force and how, prior to that, productive subjects who can properly bear and dispose of their labour power are formed. Foucault’s reading of Capital resonates with those currents of Marx interpretation today that seek to repoliticize the concept of productive force and to offer a materialist account of subject formation.