Funded by the National Institute of Justice, the Multi-Site Adult Drug Court Evaluation is a comprehensive study of outcomes at 23 drug courts and six comparison jurisdictions around the country. The study found that adult drug courts substantially reduce crime and drug use and produce a particularly large return on investment (in terms of both recidivism reductions and cost savings) among offenders who are a high risk of re-offending. This brief article summarizes the study findings and discusses their policy implications. Published in Judicature.