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This paper argues that Industrial Organization theory is essential but not sufficient to understand the individual and collective performance of modern media organizations. Institutional economics is an important source of theory, too. Whereas Industrial organization emphasizes market structural conditions that stimulate strategic variety and product differentiation, institutional economics emphasizes institutional conditions that require companies to be similar. A discussion of the basic assumptions of industrial organization and institutional economics, followed by an extensive review of media performance studies in these traditions, substantiates and illustrates this claim. The paper concludes with a number of hypotheses for future media market performance research.