This book expands our understanding of the distinctive policy analysis produced between 1919 and 1950 by economists and other social scientists for four major international organizations: the League of Nations, the International Labor Organization, the Bank for International Settlements, and the United Nations. These practitioners included some of the twentieth century's eminent economists, including Cassel, Haberler, Kalecki, Meade, Morgenstern, Nurkse, Ohlin, Tinbergen, and Viner. Irving Fisher and John Maynard Keynes also influenced the work of these organizations. Topics covered include: the relationship between economics and policy analysis in international organizations; business cycle research; the role and conduct of monetary policy; public investment; trade policy; social and labor economics; international finance; the coordination problem in international macroeconomic policy; full employment economics; and the rich-country-poor-country debate. Normative agendas underlying international political economy are made explicit, and lessons are distilled for today's debates on international economic integration.