"In recent years economists and historians have increasingly turned their attention to modern economic institutions. Economists such as Edward S. Mason, A. D. H. Kaplan, John Kenneth Galbraith, Oliver E. Williamson, William J. Baumol, Robin L. Marris, Edith T. Penrose, Robert T. Averitt, and R. Joseph Monsen, following the pioneering work of Adolph A. Berle, Jr., and Gardiner C. Means, have studied the operations and actions of modern business enterprise. They have not attempted, however, to examine its historical development, nor has their work yet had a major impact on economic theory. The firm remains essentially a unit of production, and the theory of the firm a theory of production."