The phrase 'evidence-based policy' is frequently used, but it's crucial that such claims are scrutinized and validated. When the data on social and behavioral interventions are presented, high-quality evidence must be clearly defined and the methodology behind such studies held to rigorous standards. ''Both the Cochrane Collaboration ûfocusing on healthcare û and the international Campbell Collaboration û concentrating on criminal justice, education, and social services û were   created to develop, maintain and improve detailed guidelines for producing high-quality systematic reviews. And both organizations emphasize randomized controlled trials to evaluate the effectiveness of various interventions. ''As a springboard from the Campbell Collaboration initiative and supported by the Rockefeller Foundation, this special issue of The Annals includes a thorough review of randomized tests across a variety of studies. Exploring significant dimensions of place randomized trials (also called cluster randomized trials or group randomized trials), these papers shed light on recent efforts to enhance the quality of designing such trials as well as on results reporting. ''The research topics included in this volume are diverse. Taken together, these papers offer important insight into the nuts and bolts of conducting randomized trials: the significance of place in trials; how such studies are initiated; the incentives and justifications needed by participants; how to overcome challenges of implementation; and where to find out what studies have already been conducted or are currently underway. ''While providing far-reaching insight into the topic of randomized testing, these papers also identify new issues and key questions to be further addressed in future research. Scholars and policymakers alike will find this collection of rigorous research essential in understanding the implications of current evidence-based policies as well as a guidepost for designing and conducting new studies.