This paper surveys the theoretical and empirical literature on group lending programs in developing countries, with a focus on the determinants of repayment performance. About the Author: Joel M. Guttman is a Senior Fellow at Networks Financial Institute. Guttman is currently serving as an associate professor in the department of economics in Bar-Ilan University. He has also served as a visiting professor at the University of Chicago, Brown University and the Helsinki School of Economics. His research areas include evolution of trust and cooperation, economic growth and conflict (internal and external), public economics, applied game theory, and defense economics. He has published numerous articles in scholarly journals including American Economic Review, Journal of Political Economy, Journal of Public Economics, and Economic Journal. He received his Ph.D. in economics from the University of Chicago.