This chapter discusses the history and future of prevention of mental disorders. The history of successful prevention efforts includes important disorders such as scurvy, pellagra, delirium tremens, and general paresis. The three-tiered approach of the Institute of Medicine is used (universal, selective, and indicated prevention). Successful prevention programs for the entire range of mental and behavioral disorders are reviewed at the levels of the individual, small group, family, school, workplace, community, and society. Separate sections review programs to prevent depression, schizophrenia, and cognitive decline. The Internet provides new opportunities for disseminating interventions, and integration of social, genetic, and biological predictors of mental disorders will enhance preventive efforts in the future.