AbstractNeural stem cells (NSCs) have the ability to self‐renew, and are capable of differentiating into neurones, astrocytes and oligodendrocytes. Such cells have been isolated from the developing brain and more recently from the adult central nervous system. This review aims to provide an overview of the current research in this evolving area. There is now increasing knowledge of the factors controlling the division and differentiation of NSCs during normal brain development. In addition, the cues for differentiation in vitro, and the possibility of transdifferentiation are reviewed. The discovery of these cells in the adult brain has encouraged research into their role during neurogenesis in the normal mature brain and after injury. Lastly other sources of neural precursors are discussed, and the potential for stem cells to be used in cell replacement therapy for brain injury or degenerative brain diseases with a particular emphasis on cerebral ischaemia and Parkinson's disease. Copyright © 2002 John Wiley & Sons, Ltd.