A scheme is provided for conceptualizing various approaches to prevention in relation to the Public Health Services prevention model, i.e., the Host/Agent/Environment Triad. Two different philosophies of prevention -- causes versus consequences -- are contrasted. The difficulty in prioritizing prevention approaches is discussed. Seven major areas for future prevention research are listed: (1) etiology of substance abuse, (2) efficacy of prevention programs, (3) awareness of side effects, (4) cost-effectiveness or cost-benefits, (5) clearer definitions of prevention program goals, (6) theory driven prevention and increased use of state-of-the art change technologies, and (7) increased analysis of natural experiments and existing data bases. The future of prevention, based on possible positive and negative changes in society and drug use patterns are discussed, and recommendations are made for the most promising approaches. Illustrations and 77 references. (Author abstract modified)