In the adult central nervous system (CNS), small populations of neurons are formed in the adult olfactory bulb and dentate gyrus of the hippocampus. In the adult hippocampus, newly born neurons originate from stem cells that exist in the subgranular zone of the dentate gyrus. Progeny of these putative stem cells differentiate into neurons in the granular layer within a month of the cells’ birth, and this late neurogenesis continues throughout the adult life of all mammals. Environmental stimulation can differentially effect the proliferation, migration and differentiation of these cells in vivo. These environmentally induced changes in the structural organization of the hippocampus, result in changes in electrophysiological responses in the hippocampus, as well as in hippocampal related behaviors. We are studying the cellular, molecular, as well as environmental influences that regulate neurogenesis in the adult brain. We have recently identified several molecules that work coordinately to regulate proliferation, survival and differentiation of these adult derived stem cells. In addition, we have demonstrated that specific types of activity can influence the behavior of these newly born cells. Finally, we have developed several methods to monitor the in vivo maturation of neurogenesis in vivo, which has provided insight to the functional importance of neurogenesis to behavior.  A consensus model of the function of adult neurogenesis is emerging.