Between 1940 and 1980, Ernest Mandel (1923–1995) studied many aspects of capitalism. With his magna opera, Traité d'économie marxiste (1962) and Der Spätkapitalismus (1972) he had a great impact on the social movements which emerged in the 1960s and 1970s of the last century. This article attempts to unravel the story of the development of Mandel's economic historical work. It follows the search for the synthesis of late capitalism, positions Mandel in the Marxist tradition and looks for what was innovative in his contributions. The Traité d'economie marxiste was a provocative experiment. The author shows how Mandel replaced history into the core of Marx's economic theory and how he supersedes Eurocentrism by independently asking for attention for Asia, Africa, the Islamic World and pre-Columbian America. Mandel worked on Der Spätkapitalismus for more than ten years. The article shows how Mandel rehabilitated the forgotten 'long-wave theory', which enabled him to offer an explanation for the exceptional postwar expansion, but also made him predict the end of the 'golden days of capitalism'. The study was completed in 1972 in a turbulent West Berlin, where as visiting professor at the leading Otto-Suhr-Institut für Politikwissenschaft he defended his vision in lively debate with students and confrères and where the last theoretical differences were ironed out.