In response to the magnitude of violence in the United States, a number of violence-prevention programs have been implemented throughout the country. However, relatively few have been rigorously evaluated for effectiveness. To encourage development and evaluation of violence-prevention interventions that focus on young children and their families, the Centers for Disease Control and Prevention (CDC) provided funding to four projects in 1996. This paper briefly describes the rationale for funding these projects, which is based on our understanding of the development of aggressive and violent behavior and on the literature regarding promising approaches to prevent problem behavior in this age group. We provide an overview of the four specific projects funded by the CDC as well as a short discussion of some of the many challenges encountered during their implementation.