With the general loss of interest in Marx as an analyst of capitalism, argument over the development of his thinking, from his early writings to Capital Vol. I, has given way to a more or less uncritical acceptance of Capital as the centrepiece of his endeavours, and a neglect of its sources. However, in 1913 Lenin rightly noted that there were "three sources and component parts" of "Marxism": German philosophy, English political economy, and French socialism. Curiously, few readers of Marx have taken this point seriously; while some attention has been paid to "German philosophy", little attention has been paid to the importance of Proudhon and others, while almost none at all has ever been paid to Marx’s debt to the writings of David Ricardo and Adam Smith. In this lecture, Keith Tribe seeks to readdress this imbalance in Marx scholarship.