Aggregation lies at the heart of macroeconomics. Economists using such aggregates as capital, investment, labor, and even output or GNP assume that such constructions have a sound analytic foundation. The question of the existence of aggregate production functions is not only part of the foundation of macroeconomic theory and policy but also played a central role in the "Cambridge vs. Cambridge" debate, which challenged long-held assumptions about the foundations of neoclassical microeconomics. In this third collection of his essays Franklin M. Fisher settles the question of the conditions for the existence of aggregate production functions. He examines the conditions for approximate aggregation and, through simulation experiments, considers why aggregate production functions appear to work in practice. He also explores related topics involving price aggregation and aggregation in international trade. Franklin M. Fisher is Professor of Economics at the Massachusetts Institute of...