Contrary to the way it has usually been taken, the most enduring legacy of Marx's thought is philosophical, not practical. Marx's account of political economy, of class and of revolution have occasioned legitimate criticisms, and the practical outcomes of the social movements based on Marxism have largely been negative. Without denying the power of his critique of capitalism, I will argue here that the most important and viable aspect of Marx's thought resides in some of his basic philosophical ideas - particularly the normative concepts - and the turn that they led to in political philosophy. This is somewhat ironic, of course, since on the usual view - whether Left or Right - Marx's normative, philosophical ideas are the least central and certainly the least developed part of his work, compared with the central role of his political economy and revolutionary theory.