What are the factors that shape crime and justice policy? Long-term traditions-steeped in politics, ideology, values, ethics, and faith-along with clinical experience have served as the primary guides for policymakers. However, many contemporary scholars, practitioners, and policymakers encourage heavier reliance on scientific research to form crime and justice policy. ''Along with this shift toward evidence-based crime prevention, it becomes crucial for practitioners to accurately identify and understand which programs and practices have been the most effective in the past. So relying on systematic reviews of prior research and evaluation is central to the movement toward a more scientific approach to policymaking. ''The surge of research and evaluation in crime and justice raises a myriad of methodological concerns. This special issue of The ANNALS, which sprang from the Second Annual Jerry Lee Crime Prevention Symposium held at the University of Maryland in April 2002, identifies and addresses those methodological concerns and also presents substantive empirical outcomes of specific studies. ''Developed by the Campbell Collaboration Crime and Justice Group, which continues to focus on issues of evidence, this journal provides valuable insights to researchers, practitioners, and policymakers in the promotion and development of an evidence-based approach to crime and justice policy and practice.