This volume is based on a meeting of the Fondation IPSEN, held in Paris on Sep tember 18, 1995 to address the main issues of nervous system stem cells biology. Cell replacement in the adult mammals is not unusual outside the nervous sys tem. In fact, the nervous system is unique in lacking the ability to replace cells, following damage. Most neurons, in the adult central nervous system are termin of the organism and are not replaced ally differentiated, exist through the life when they die. There are, however, regions of the postnatal brain that continue to produce new neurons, but the fate...