Most studies on childhood mental disorders have been conducted retrospectively. Prospective studies on the etiology of childhood mental illness provide a necessary opportunity to consider developmental contributions, but the literature using a developmental approach is sparse. Animal studies using a developmental framework for studies of brain and behavior may be helpful in expanding our understanding of some childhood disorders. Considerable attention has been focused on understanding genomic sources of vulnerability to mental illness. However, the development of brain and behavior is the essential link between genes, their products, and ultimately their functional expression. Current diagnostic practice for children's mental health is limited by the absence of independent biological or behavioral criteria guiding clinical decisions. The object of this volume is to build bridges between animal research and clinical approaches for studying mental health and disorders in children and adolescents.