Recent advances in the field of prevention have led to a deeper understanding of the causes of adolescent problem behavior and to the identification of efficacious strategies to prevent delinquency, drug use, and other antisocial conduct. This 2009 Aaron Rosen lecture to members of the "Society for Social Work and Research" traces the evolution of prevention approaches in the United States. A public health model of intervention based on the principles of risk and protection is introduced as an important development in the field of prevention science. Examples from two longitudinal studies are used to illustrate how advances in prevention have led to positive changes in the lives of vulnerable children and youth. Practice, policy, and research challenges necessary to increase the impact of prevention are discussed. (Contains 2 tables and 6 figures.)