There is a growing appreciation for the neurodevelopmental underpinnings of many psychiatric disorders. While the importance of the growth and structuring of the brain has long been recognized for disorders that begin in childhood such as autism, language disorders or mental retardation, there is consensus building that adult-onset mental disorders also have origins early in neurodevelopment. In order to expand our understanding of these origins, the National Institute of Mental Health (NIMH) is investing in studies of developmental neurobiology, choosing one of its strategies to be the support of “research to improve our basic understanding of the development, structure, and function of neural circuits, with a focus on those most relevant to mental disorders” (NAMHC, 2008). Forwarding this agenda requires a better understanding of the neurobiology of neural stem cells (NSCs) and the factors that regulate them in the developing brain.