This article aims at identifying the main features of current mutations of capital/labour relation, which revolves around the shift from the Fordist working relations to one based on immaterial and cognitive labour. The analysis is organised in three sections. The first section is devoted to the presentation of method and concepts of a post-operaist analysis of dynamics of capitalism. This approach permits to highlight the role knowledge play in the capital/labour relation. So doing, we point to some theorical and political implications in terms of historical meaning of the law of value. The following two sections analyse historically the crisis of Fordism and the passage to a cognitive capitalism. Finally, we show how the role more and mor...