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 … central features of antitrust policy. Our objective is to foster the improvement of legal regimes and also to identify topics …

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 … coordinated and unilateral competitive effects of merger. The central issue considered is when and how market shares, and market …