In this Introduction I illuminate the importance of Nicos Poulantzas’s participation at a 1967 colloquium in Frankfurt commemorating the 100th anniversary of the publication of Capital. This colloquium is the only published record of a dialogue between a representative of Louis Althusser’s interpretation of Marx and a member of the first generation of the Frankfurt School and thus casts light on the relationship between these two traditions of critical social theory. After contextualising the colloquium and summarising Poulantzas’s paper, I outline (...) some of the elements of the Frankfurt response to the Althusserian interpretation of Marx by referring to Alfred Schmidt’s contribution to the colloquium, including his reaction to Poulantzas’s paper. (shrink)