Monitoring the well-being of children and adolescents is a critical component of efforts to prevent psychological, behavioral, and health problems and to promote their successful development. Research during the past 40 years has helped identify aspects of child and adolescent functioning that are important to monitor. These aspects, which encompass family, peer, school, and neighborhood influences, have been shown to be associated with both positive and negative outcomes for youth. As systems for monitoring well-being become more available, communities will become better able to support prevention efforts and select prevention practices that meet community-specific needs. There is evidence that supports the importance of certain factors for young people to function successfully including academic success and participation in volunteer activities. Research also has identified biological, psychological, and social factors that are associated with negative outcomes in youth; these include substance use, antisocial behavior, risky sexual practices, and academic failure. From a public health perspective, the problems most important to monitor can be chosen based on their prevalence and consequences to youth, their families, and communities. Communities can choose which factors to monitor based on the prevalence and consequences of these factors in their community. This monograph describes Federal, State, and local monitoring systems that provide estimates of problem prevalence; risk and protective factors; and profiles regarding mobility, economic status, and public safety indicators. Data for these systems come from surveys of adolescents and archival records. A list of resources is included. (Contains 2 tables and 7 figures.) [Funding from the National Institutes of Health and Robert Wood Johnson Foundation--coordinated through the National Science Foundation and the Society for Prevention Research--supported the preparation of the original version of this monograph. The original version of this document was written by Patricia Mrazek, M.S.W., Ph.D., Anthony Biglan, Ph.D., J. David Hawkins, Ph.D., and Christine Cody; the edited version was prepared by National Institute on Drug Abuse (NIDA).]