Following a general orientation to prevention concepts and program strategies, the model for prevention evaluation is presented. The evaluation research model is applicable to any of the four drug abuse prevention modalities (information, education, alternatives, and early intervention) as well as any of the five primary targets (individuals, peers, families, the school, and other significant social institutions). The model features three levels of evaluation: process, outcome, and impact. Each level has its own set of indicators of effectiveness and its own appropriate evaluation methodologies. Process evaluation refers to an assessment of a prevention program that includes identification of the target population, a description of the services delivered, the use of resources for the programs, and the qualifications and experiences of the personnel participating in them. Outcome evaluation is concerned with measuring the effect of a project on the people participating in it, while impact evaluation explores the aggregate effect of prevention programs on the community as a whole. A major section of the presentation deals with methodology. After discussing general methodological issues, specific methods appropriate to the evaluation of process, outcome, and impact are considered. Many of the major statistical issues facing the evaluator are then examined, followed by descriptions of the most important data analysis strategies available and their range of applicability. The concluding major section addresses the issue of how to increase the likelihood that evaluations will be used. Chapter references and endnotes are provided.