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2026 Colum. Bus. L. Rev. 1 (2026)

handle is hein.journals/colb2026 and id is 1 raw text is: DEFINING MARKETS: A GUIDE FOR THE PERPLEXED William H. Rooney,* Taylor Owings,** Adriana Morton,*** and Yifei Xu**** To present the contextfor the 2025 TaftLecture, this article addresses the role of market definition under the antitrust Iaws, including »with repect to standing, mergers, concerted restraints of trade and monopoliation. 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. IN TRO D U CTIO N ............................................................................. 2 I. THE REQUIREMENT OF MARKET DEFINITION: FITTING THE T O O L TO TH E T ASK ......................................................................... 3 A. When Antitrust Injury Is Contested ............................... 4 B. Merger Cases (Clayton Act Section 7) ............................ 5 C. Sherman Act Section 1 Cases .......................................... 6 D. Sherman Act Section 2 Cases .......................................... 7 II. THE PERPLEXITIES OF MARKET DEFINITION: NAVIGATING CONFLICTING LEGAL CRITERIA..................................................... 9 A. The Brown Shoe Framework...............................................9 B. The 2023 Merger Guidelines ..............................................15 C. The W hole Foods D ebate ......................................................17 1. Core versus Marginal Customers.................................17 2. Special Treatment of Venue.........................................22 a. K rog er........................................................................2 4 b. Meta..........................................................................27 * William H. Rooney is a Lecturer in antitrust law at the Columbus School of Law at The Catholic University of America and a former partner of Willkie Farr & Gallagher LLP and former co-chair of the firm's U.S. Antitrust Practice. ** Taylor M. Owings is a partner in the Antitrust and Competition Practice Group of Wilson Sonsini Goodrich & Rosati. Adriana Morton is a foreign lawyer trainee at Clifford Chance. ** Yifei Xu is an antitrust associate of Wilson Sonsini Goodrich & Rosati.