John Donaldson is Mario J. Gabelli Professor of Economics and Finance at the Graduate School of Business, Columbia University. He received his Ph.D. from Carnegie-Mellon University’s Graduate School of Industrial Administration, and has taught at Columbia since his graduation. His research papers, many of them coauthored with Jean-Pierre Danthine and Rajnish Mehra, have appeared in Econometrica, the Journal of Economic Theory, the Quarterly Journal of Economics, the Journal of Economic Dynamics and Control, Economic Theory, The International Economic Review, and many others.