Richard R. Nelson is Henry R. Luce Professor of International Political Economy at Columbia University. His research has concentrated on the processes of long-run economic change, with particular emphasis on technological advances and on the evolution of economic institutions. His recent publications include "R & D, Knowledge, and Externalities: An Approach to the Puzzle of Disparate Productivity Growth Rates Among Manufacturing Industries," "Firm and Industry Response to Changed Market Conditions: An Evolutionary Approach," and "Technical Advance and Productivity Growth: Retrospect, Prospect, and Policy Issues."