Steven G. Medema is a Research Professor at Duke University. His research focuses on the History of Economic Thought, having published extensively on the issue of social costs of production (conceptualized as externalities in neoclassical economics). In this recorded seminar, he exposes his working paper on the history of the concept of externalities in economic literature, starting from Pigou’s “The Economics of Welfare” (1920), where Pigou makes the case for governmental intervention in the market where there is a divergence between private and social costs or benefits of a productive activity. T