HKS Affiliated Authors


Summer 2022, Paper: "The Supreme Court Decision in Ohio v. American Express Co.,1 has sparked more than its share of controversy. Indeed, the decision has been described as “what may be the worst antitrust decision in many decades.”2 The Court ruled that the product market for use of credit cards needed to be defined to include both cardholders and the merchants that accepted those cards, and that because the plaintiffs did not establish harm in that relevant market, they thereby failed to establish a prima facie case that would require the defendant to offer evidence justifying its conduct.3 In a manner not contemplated by past Supreme Court precedent, the Amex Court introduced a new measure of market definition, based on the presence of “transaction platforms.”