This report summarizes the presentations and discussion at a workshop entitled Opportunities to Promote Child and Adolescent Development During the After-School Hours, convened on October 21, 1999. The workshop was organized by the Board on Children, Youth, and Families and its Forum on Adolescence of the National Research Council and the Institute of Medicine, with funding from the David and Lucile Packard Foundation. This workshop brought together policy makers, researchers, and practitioners to examine research on the developmental needs of children and adolescentsâ€"ages 5 to 14 yearsâ€"and the types of after-school programs designed to promote the health and development of these young people. Intended to provide a forum for discussion among the various stakeholders, the workshop did not generate conclusions about the types of programs that are most effective, nor did it generate specific recommendations about after-school programs or promote a particular approach. The workshop coincided with release of the Packard Foundation's fall 1999 issue of The Future of Children, entitled "When School Is Out." Focusing on after-school programs, the journal provided some context for the workshop, providing a backdrop for discussing the importance of after-school programs, the types of programs that exist across the country, and the policy climate that surrounds after-school programs. This report summarizes the workshop.