This handbook chapter appears in Antitrust Law & Economics (Keith Hylton, ed. 2010). It describes the role of market concentration in the legal framework for the antitrust review of horizontal mergers and evaluates the extent to which modern economic analysis supports a role for concentration in...

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...

This article takes a fresh look at a longstanding issue in antitrust economics and policy: the problem of oligopoly coordination. First, it explains why coordinated conduct in oligopoly markets is a serious problem and an appropriate concern of antitrust enforcement. It shows that empirical...

This article explains the inherent loss of an indirect competitor and reduction in competition when a vertical merger raises input foreclosure concerns. We then calculate a measure of the effective increase in the HHI measure of concentration for the downstream market, and we refer to this...