The Amex Decision and the Future of Antitrust for Two-Sided Platforms

This article discusses the recent Second Circuit decision in the Justice Department's antitrust case against American Express (Amex). The decision has important implications for antitrust in all industries involving two-sided platforms. The article focuses on the issues of market definition, market power, and anticompetitive effects. The decision stresses the importance of looking at both sides of the market when considering each of these issues. As a result, antitrust enforcement will be more difficult but also better. By requiring a full analysis of the effects of challenged behavior on all groups of a platform's customers, the decision may prevent actions against behavior that significantly benefits consumers