The article aims to reinterpret the relationship between Louis Althusser and Michel Foucault on the specific ground of the notion of " Ideology." If Foucault's critique addresses initially the alleged opposition between ideological discourse and scientific discourse , this does not seem to fade in the seventies, despite the convergence of Foucault 's " microphysics of power" with Althusser 's insistence on the "material" character of ideology. To explain the persistence of this comparison and of this tension the author shows (...) how with it are involved highly problematic knots for the whole Foucault's thought : the status of representation and truth , the inner existence and temporality of capitalism and , in particular , the relationship between criticism and politics. (shrink)