To establish a genetic tool for manipulating the neural stem/progenitor cell (NSC) lineage in a temporally controlled manner, we generated a transgenic mouse line carrying an NSC-specific nestin promoter/enhancer expressing a fusion protein encoding Cre recombinase coupled to modified estrogen receptor ligand-binding domain (ER(T2)). In the background of the Cre reporter mouse strain Rosa26(lacZ), we show that the fusion CreER(T2) recombinase is normally silent but can be activated by the estrogen analog tamoxifen both in utero, in infancy, and in adulthood. As assayed by beta-galactosidase activity in embryonic stages, tamoxifen activates Cre recombinase exclusively in neurogenic cells and their progeny. This property persists in adult mice, but Cre activity can also be detected in granule neurons and Bergmann glia at the anterior of the cerebellum, in piriform cortex, optic nerve, and some peripheral ganglia. No obvious Cre activity was observed outside of the nervous system. Thus, the nestin regulated inducible Cre mouse line provides a powerful tool for studying the physiology and lineage of NSCs.