The existence of adult stem cells was first described in tissues with high proliferation rates, such as the hematopoietic system and the intestine. Since then, stem cells have been found in almost all adult tissues, including the nervous system. Adult neurogenesis is supported by multipotent neural stem cells (NSCs), which maintain some of the cellular and molecular characteristics of their embryonic counterparts. Because of their suggestive appeal as therapeutic agents and their presumed relevance for cognition in health and disease, adult neurogenesis is attracting considerable attention from neuroscientists.