This book examines the academic life of Oskar Lange and his contribution to economics. It charts the development of his ideas across his working life and reflects on how the events of this period shaped his view of economics. His early engagement with European Marxism during the 1920s is outlined, as well as the ways that the 1929 economic crash encouraged Lange to evaluate the social dimension of economics and consider the economic underpinnings of a socialist planned economy. Lange’s engagement with debates surrounding the theory of production, capital, the theory of interest, welfare economics, and general equilibrium during the 1930s and 1940s are outlined and provide insight into how Lange viewed the key economic debates of the day. The legacy of Lange, not just within socialist economics, but within the discipline more generally, is discussed to reflect upon his place within the Marxist tradition and his relevance within modern economics. This book offers unique insight into the work and legacy of Oskar Lange. It will be of interest to students and researchers working within the history of economic thought and the political economy.