Systematic reviews have, increasingly, informed policy for almost 3 decades. In many countries, systematic reviews have informed policy for public and population health, paying for health care, increasing the quality and efficiency of interventions, and improving the effectiveness of health sector professionals and the organizations in which they work. Systematic reviews also inform other policy areas: criminal justice, education, social welfare, and the regulation of toxins in the environment. Although the production and use of systematic reviews has steadily increased, many clinicians, public health officials, representatives of commercial organizations, and, consequently, policymakers who are responsive to them, have been reluctant to use these reviews to inform policy; others have actively opposed using them. Systematic reviews could inform policy more effectively with changes to current practices and the assumptions that sustain these practices-assumptions made by researchers and the organizations that employ them, by public and private funders of systematic reviews, and by organizations that finance, set priorities and standards for, and publish them.