Over a decade ago, a concerted effort was made by members of the criminology community, including the editors and contributors of this volume, to bring the practice of systematic reviews to the study of criminology, in order to provide replicable, evidence-based data to answer key questions about the study of crime causation, detection, and prevention. Here, the pioneers in this effort present a comprehensive stock-taking of what has been learned, bringing together and assessing all major systematic reviews of the effectiveness of criminological interventions, to draw broad conclusions about what works in policing, corrections, developmental prevention, situational prevention, drug abuse treatments, sentencing and deterrence, and communities.