Evidence-based policy has much to recommend it, but it also faces significant challenges. These challenges reside not only in the dilemmas faced by policy makers but also in the quality of the evaluation evidence. Some of these problems are most effectively addressed by rigorous syntheses of the literature known as systematic reviews. Other problems remain, including the range of quality in systematic reviews and their general failure to be updated in light of new evidence or disseminated beyond the research community. Based on the precedent established in health care by the international Cochrane Collaboration, the newly formed Campbell Collaboration will prepare, maintain, and make accessible systematic reviews of research on the effects of social and educational interventions. Through mechanisms such as rigorous quality control, electronic publication, and worldwide coverage of the literature, the Campbell Collaboration seeks to meet challenges posed by evidence-based policy. Downloaded from 15 DONALD Campbell (1969) was an influential psychologist who wrote persuasively about the need for governments to take evaluation evidence into account in decisions about social programs. He also recognized, however, the limitations of the evidence-based approach and the fact that government officials would be faced with a number of political dilemmas that confined their use of research. The limits of evidence-based policy and practice, however, reside not only in the political pressures faced by decision makers when implementing laws and administrative directives or determining budgets; they also reside in problems with the research evidence.Questions such as, What works to reduce crime in communities? are not easily answered. The studies that bear on these questions are often scattered across different fields and written in different languages, are sometimes disseminated in obscure or inaccessible outlets, and can be of such questionable quality that interpretation is risky at best. How can policy and practice be informed, if not persuaded, by such a fragmented knowledge base comprising evaluative studies that range in quality? Which study, or set of studies, if any at all, ought to be used to influence policy? What methods ought to be used to appraise and analyze a set of separate studies bearing on the same question? And how can the findings be disseminated in such a way that the very people Donald Campbell cared about-the decision makers in government and elsewhere-receive findings from these analyses that they trust were not the product of advocacy? Donald Campbell unfortunately did not live long enough to bear witness to the creation of the international collaboration named in his honor that ambitiously attempts to address some of the challenges posed by evidence-based policy. The Campbell Collaboration was created to prepare, update, and disseminate systematic reviews of evidence on what works relevant to social and educational intervention (see http:// campbell.gse.upenn.edu). The target audience will include de...