Drug courts emerged in the late 1980s in response to rapidly increasing felony drug caseloads that strained the Nation's courts and overflowed its jails and prisons. Their goal is to reduce substance abuse and criminal behavior and free the court and correctional systems to handle other cases. By providing a structure that links supervision and treatment as an alternative to incarceration, drug courts exert legal pressure on defendants to enter and remain in treatment long enough to realize benefits. As of December 2005, more than 1,500 drug courts were operating in the United States and another 391 were being planned. As part of the evaluation of these courts, researchers have begun to look at their inner workings and to investigate how key functional components, singly and in combination, affect outcomes. This NIJ Special Report presents findings from several recent studies that speak to the concerns of policymakers and practitioners about "what works" in drug courts. Topics addressed include how target populations and participant attributes affect program outcomes, the judge's role in the success of drug court participants, treatment issues, drug court interventions for juveniles, and cost-benefit analyses of drug courts.