Oliver E. Williamson is a highly distinguished business economist and the author or editor of several books and articles, most famous being Markets and Hierarchies (The Free Press, New York, 1975). He recently edited another book for Oxford, Organizational Theory: From Chester Barnard to the Present and Beyond (1990). He has taught at the University of Pennsylvania (1965-77), Yale University (1983-8), the University of Warwick (1973), the University of Kyoto (1983), Harvard University (1987), Indiana University (1987). He has also delivered lectures at a wide range of universities, including, in Europe Lund and Madrid Univeristies. He is on the Editorial Boards of several journals: Journal of Law, Economics, and Organization; Journal of Economic Organization; Journal of Japanese and International Economics; Journal of Accounting, Auditing, and Finance; Organization Studies; Regulation; Organization Science; and Cambridge Surveys of Economic Literature. He is a Fellow of the Econometric Society. Ronald Coase won the Nobel Prize for Economics in 1991 for achieving a `breakthrough in understanding the institutional structure of the economy'. He taught at the London School of Economics from 1935-51, where he produced `The Nature of the Firm' (1937), which has had a profound effect on economists. He is well known to economists for the Coase Theorem, which he presented in a pathbreaking paper in 1960. He comes from Middlesex, but emigrated to America and he has held posts at the University of Chicago Law School for several years. Oliver D. Hart, who recently delivered the Clarendon Lectures in Economics at Oxford, is at Massachusetts Institute of Technology, as is Paul L. Joskow. Benjamin Klein is at the University of California, Los Angeles; Scott E. Masten is at the University of Michigan; and Sherwin Rosen is at the University of Chicago.