In the central nervous system, neuron generation continues throughout adulthood. This neurogenesis is involved in a continual adaptative process in relation with the environmental complexity. It decreases with age and is reduced in several types of experimental conditions mimicking stress, depression, addiction and neurodegenerative diseases. It may be enhanced after excitotoxic, ischemic or traumatic injuries suggesting a compensatory adaptative response. Available data on this new concept in the field of neurosciences and possible therapeutic relevance are reported.