Market power is the most important determinant of liability in competition law cases throughout the world. Yet fundamental questions on the relevance of market power are underanalyzed, if examined at all: When and why should we inquire into market power? How much should we require? Should market...

Market definition has long held a central place in competition law. This entry surveys recent analytical work that has called the market definition paradigm into question on a number of fronts: whether the process is feasible, whether market share threshold tests are coherent, whether the...

This is a survey of the economic principles that underlie antitrust law and how those principles relate to competition policy. We address four core subject areas: market power, collusion, mergers between competitors, and monopolization. In each area, we select the most relevant portions of...

In competition law, market power requirements are often articulated in terms of market shares. The use of market share thresholds, however, conflates two distinct questions: (1) How much market power exists in a given situation? (2) How much market power should the law require? As a consequence,...

Market definition and market power are central features of competition law and practice but pose serious challenges. On one hand, market definition suffers decisive logical infirmities that render it infeasible, unnecessary, and counterproductive, and the practice of stating market power...

The recently issued revision of the U.S. Horizontal Merger Guidelines, like its predecessors and mirrored by similar guidelines throughout the world, devotes substantial attention to the market definition process and the implications of market shares in the market that is selected. Nevertheless,...

Does significant market power or the presence of large rents affect optimal income taxation, calling for greater redistribution due to tainted gains? Or perhaps less because of an additional wedge that distorts labor effort? Do concerns about inequality have implications for antitrust,...

In recent articles, I have advanced a number of criticisms of the market definition/redefinition paradigm, chief among them that market definition is impossible and counterproductive. First, there is no valid way to infer market power from market shares in redefined (non-homogeneous-goods)...