Not So Fast, You Still Have to Define the Relevant Market: The Less Debated Yet Vital Teaching of Ohio v. American Express

By Elai Katz

Most discussions of Ohio v. America Express focus on two-sided markets. This article will not. Instead, the article analyzes the Court’s ruling that plaintiffs cannot evade defining the relevant market when challenging vertical restraints (and arguably other practices subject to the rule-of-reason). In holding that courts must first define the relevant market before assessing evidence of anticompetitive effects in rule-of-reason cases, the majority resisted efforts to relax the m