As used in this guide, risk assessment refers to "the practice of using a structured tool that combines information about youth to classify them as being low, moderate, or high risk for reoffending or continued delinquent activity, as well as identifying factors that might reduce that risk on an individual basis." The recommendations presented in this guide are based in research that has shown their effectiveness when implemented. This guide is published as part of the John D. and Catherine T. MacArthur Foundation's Models for Change Initiative, which is a national juvenile justice reform initiative in 16 States; the program began in 2005. The risk assessment tools described in this guide are not appropriate for the identification of risk for sexual offenses. Such offenses require a distinctive psychological evaluation or more specialized risk assessment tools. Neither do the proposed tools constitute mental health assessments or prescriptions for legal decisions. They are intended to minimize bias in judgments about youths' risk to public safety and identify their case-management needs. In addition, they can reduce costs by decreasing the use of more intensive supervision; the over-use of expensive incarceration; and the provision of services for youth who do not need them. Further, the tools can improve resource development by providing a means for objective data used in monitoring the primary problems for a youth. Most importantly, risk assessment tools are a cost-effective means of reducing reoffending rates. The guide's chapters explain the purpose and nature of risk assessment, provides definitions of risk assessment concepts, reviews research evidence, and offers step-by-step guidance on how to implement a tool.