Even in the adult brain, new neurons are continuously generated from endogenous neural stem cells that reside in two restricted regions: the subventricular zone (SVZ) of the lateral ventricle and the dentate gyrus of the hippocampus. These new neurons are integrated into the mature neuronal circuitry and become involved in various functions, thereby contributing to structural and functional plasticity in the adult brain. In this review, we summarize our recent findings on the regulatory mechanisms of SVZ neurogenesis under physiological and pathological conditions in various animal models. Some of these findings were presented in the Kitazato Prize Lecture at Keio University School of Medicine in 2011.