The debate on the structure of Marx's Capital, and on the probable explanations for the changes he made to the initial ‘six books plan’, has always been a relevant topic in Marxist studies. This article provides a more exhaustive account of the genesis of Capital, on the basis of a revisitation of Marx's intellectual biography during the 1860s, and of the publication of all preparatory manuscripts of Marx's magnum opus, recently appeared in the MEGA2, the historical-critical edition of the complete works of Marx and Engels.