Defining Markets: A Guide for the Perplexed

Abstract

To present the context for the 2025 Taft Lecture, this article addresses the role of market definition under the antitrust laws, including with respect to standing, mergers, concerted restraints of trade and monopolization. The article also addresses some of the “perplexities” of the legal criteria for market definition, focusing on Supreme Court and subsequent case law, the FTC and DOJ 2023 Merger Guidelines, and recent merger cases. We address the relevance of Brown Shoe's “practical indicia” as well as of “core” and “marginal” consumers to market definition.