A substantial knowledge base exists on reduction of tobacco use by youth. Effective prevention in this area can have major health and economic benefits. Information from research and prevention practice, organized by means of the Prevention Enhancement Protocols System (PEPS), is provided in the form of guidelines and recommendations for planning prevention programs. Topics presented are: (1) "How Did PEPS Develop the Practitioner's Guide?"; (2) "Why Focus on Tobacco Use among Youth"; (3) "How Big a Problem is Tobacco Use among Youth?"; (4) "General Recommendations: How Can Practitioners Have the Greatest Impact?" which makes suggestions for planning and implementing a successful prevention program; and (5) "What Works? Six PEPS Prevention Approaches." Six types of interventions are outlined: economic interventions, counteradvertising, retailer-directed interventions, multicomponent school-linked community approaches, tobacco-free environment policies, and restriction of advertising and promotion. The following information is presented for each approach: the goals of the intervention, rationale, objectives and activities of studies reviewed, level of evidence, and lessons learned from reviewed evidence. Several recommendations for practice are provided from the PEPS expert panel for each approach. Appendixes are: "Criteria for Establishing Levels of Evidence of Effectiveness,""Abbreviations and Glossary," and "Resource Guide." (EMK)