This presentation focuses on Marx’s theoretical production during his 1843-45 Paris stay. The discovery of the proletariat and of revolution, the adhesion to communism, the criticisms of Hegel’s speculative philosophy and of the Hegelian Left; the first delineation of a materialistic conception of history and his “landing” to the critique of political economy, account for the entire set of fundamental themes on which Marx focused his attention during this period.