The macroeconomics of imperect competition has become in recent years a most influential paradigm, which many macroeconomists now prefer to the "Classical" of "Keynesian" ones, notably because of its clear and rigorous microfoundations. This volume collects and puts into perspective the leading contributions to this important and rapidly expanding field. It contains 28 articles, dating from 1939 to 1991. Contributors include: T.M. Anderson, R. Barro, H. Dixon, W. Leontief, T. Negishi and H. Sneessens.