Since the Supreme Court's landmark 1963 decision in Philadelphia National Bank, antitrust challengers have mounted prima facie cases against horizontal mergers that rested on the level and increase in market concentration caused by the merger, with proponents of the merger then permitted to...

“Horizontal shareholding” occurs when one or more equity funds own shares of competitors operating in a concentrated product market. For example, the four largest mutual fund companies might be large shareholders of all the major United States air carriers. A growing body of empirical...

In August, 2010, the Antitrust Division and the Federal Trade Commission issued new Guidelines for assessing the competitive effects of horizontal mergers under the antitrust laws. These Guidelines were long awaited not merely because of the lengthy interval between them and previous Guidelines...

We study how the courts have responded to the 2010 Horizontal Merger Guidelines issued by the U.S. Department of Justice and the Federal Trade Commission. Looking at decided cases, we find that both the government and merging parties rely on the 2010 Guidelines in presenting their cases, each...

This is a survey of the economic principles that underlie antitrust law and how those principles relate to competition policy. We address four core subject areas: market power, collusion, mergers between competitors, and monopolization. In each area, we select the most relevant portions of...

The past forty years have witnessed a remarkable transformation in horizontal merger enforcement in the United States. With no change in the underlying statute, the Clayton Act, the weight given to market concentration by the federal courts and by the federal antitrust agencies has declined...

Three years ago, the Antitrust Division and the Federal Trade Commission revised their Horizontal Merger Guidelines to articulate in greater detail how they would treat claims of efficiencies associated with horizontal mergers: claims that are frequently made, as for instance in the recently...