When first published a quarter of a century ago, Richard Posner's exposition and defense of an economic approach to antitrust law was a challenge to prevailing conceptions of antitrust policy. Since then, and in part as a result of the influence of the first edition, the antitrust field has been largely, although not completely, transformed into a body of economically rational principles consistent with the ideas set forth in the book. Today's antitrust professionals disagree on specific practices and rules, but most litigators, prosecutors, judges, and scholars agree that the primary goal of antitrust laws should be to promote economic welfare, and that economic theory should be used to determine how well business practices conform to that goal. In this extensively revised edition, Posner explains the economic approach to new generations of lawyers and students. He updates and amplifies his approach as it applies to the developments, both legal and economic, in the antitrust field since 1976. The "new economy," for example, has presented a host of difficult antitrust questions, and a new chapter explains how the economic approach can be applied to it. "The antitrust laws are here to stay," Posner writes, "and the practical question is how to administer them better-more rationally, more accurately, more expeditiously, more efficiently." This fully revised classic will continue to be a standard work in the field.