Ronald H. Coase was one of the most innovative and provocative economists of the twentieth century. Besides his best known papers on ‘The Nature of the Firm’ and ‘The Problem of Social Cost’, he had a major role in the development of the field of law and economics, and made numerous influential contributions to topics including public utilities, regulation and the functioning of markets. In this comprehensive Companion, 31 leading economists, social scientists and legal scholars assess the impact of his work with particular reference to the research programs initiated, the influence on policymakers, and the challenge to conventional perspectives.