There is an extensive body of research on the factors that predict mental health and illness, focusing on factors within the adolescent as well as within the various components of the adolescents environment. This paper presents a selective review of the research pertaining to each layer of the adolescent's internal and external world. Throughout this paper, the aim is to go beyond the broad identification of which factors appear to be linked to mental health and illness, to the identification of specific strategies that have been attempted and evaluated, and/or for which there is evidence that initiating programs with these activities has the potential to contribute to improved mental health. These studies reveal that individual, family, peer, neighborhood, and media level variables have been found to predict both internalizing and externalizing problems. With this in mind, programs should be aware of the following: multi-component interventions appear to be the most effective for preventing and intervening in externalizing disorders; psychotherapy, pharmacotherapy and community-level strategies appear to be effective in reducing internalizing disorders; starting prevention programs as early as possible is an important approach to preventing mental disorders and externalizing problems in adolescence; research into positive mental health is particularly sparse for adolescents; more experimental evaluations of treatments and preventions are needed. (Contains 178 references and 2 tables.) (GCP)