In recent years, federal courts have become increasingly aggressive in shaping regulatory policy, abandoning their traditional deference to bureaucratic expertise. This new judicial activism has been particular evident in the regulation of air pollution. R. Shep Melnick analyzes the effects a variety of court decisions have had on federal air pollution control policy and assesses the courts’ institutional capacity for policymaking in such a complex arena. In six cases studies of environmental programs or issues he examines the interplay among the courts, the Environmental Protection Agency, Congress, and the White House. The conventional wisdom is that the courts have improved environmental policymaking, but Melnick concludes that as a whole “the consequences of court action under the Clean Air Act are neither random nor beneficial.” He finds that “court action has encouraged legislators and administrators to establish goals without considering how they can be achieved,” widening the gap between promise and performance. The results, he charges, have been increased cynicism, serious inefficiencies and inequities, and a lack of rational debate. An analysis of the institutional characteristics of the judicial branch reveals how these problems have come about and why they are likely to afflict other programs as well as environmental regulation. The author proposes several reforms to improve the courts’ ability to handle regulatory cases.