This monograph is a guide to effective problem behavior prevention programs for at-risk youth. The monograph discusses the level and characteristics of adolescent risk-taking today, common elements of successful prevention programs along with an explanation of criteria used to evaluate programs, the challenges facing practitioners trying to replicate promising programs and suggestions for meeting those challenges, and a prevention readiness questionnaire. The monograph presents profiles of 51 prevention programs whose behavioral evaluations demonstrate their effectiveness. The profiles provide general information about the programs, highlight unique features, summarize evaluation results, and give contact information. Curriculum and training as well as contact information are provided for the subgroup of 21 most rigorously investigated programs. A reference chart is included for quick comparison of the programs.