As physicians explore areas of diversification and networking that can position them favorably for the changing health-care environment, their fear of running afoul of antitrust legislation handicaps them. A basic understanding of the intent of antitrust legislation and its application to healthcare is essential to physicians' strategic planning. This article traces the development of antitrust legislation and the regulatory agencies charged with its oversight. The authors review the first application of this legislation to the professions; distinguish per se violations from the rule-of-reason process; and summarize recent attempts by the Department of Justice and the Federal Trade Commission to provide useful guidance to healthcare providers in the market revolution.