Introduction, 132. — I. Requirements for entry, 134. — II. Oligopolistic uncertainties and large-firm entry, 137. — III. Effects on market performance of entry by outside firms, 139. — IV. A parenthesis on mergers, 143. — V. Social effects: career opportunities, 145. — VI. Business size and “concentration of power,” 147. — VII. Summary and conclusions, 149.