The health care industry is being transformed. Large firms are merging and acquiring other firms. Alliances and contractual relations between players in this market are shifting rapidly. Within the next few years, many markets are predicted to be dominated by a few large firms. Antitrust enforcement authorities like the Department of Justice and the Federal Trade Commission, as well as courts and legislators at both the federal and state levels, are struggling with the implications of these changes for the nature and consequences of competition in health care markets. In this paper we summarize the nature of the changes in the structure of the health care industry. We focus on the markets for health insurance, hospital services, and physician services. We then discuss the potential implications of the restructuring of the health care industry for competition, efficiency, and public policy. As will become apparent, this area offers a number of intriguing questions for inquisitive researchers.