In 1965, a group of economists at Harvard University established the Project for Quantitative Research in Economic Development in the Center for International Affairs. Brought together by a common background of fieldwork in developing countries and a desire to apply modern techniques of quantitative analysis to the policy problems of these countries, they produced this volume, which represents that part of their research devoted to formulating operational ways of thinking about development problems. The seventeen essays are organized into four sections: General Planning Models, International Trade and External Resources, Sectoral Planning, and Empirical Bases for Development Programs. They raise some central questions: To what extent can capital and labor substitute for each other? Does development require fixed inputs of engineers and other specialists in each sector or are skills highly substitutable? Is the trade gap a structural phenomenon or merely evidence of an overvalued exchange rate? To what extent do consumers respond to changes in relative prices?