Resident among the highly structured adult nervous system, a few cells, referred to as neural progenitors or stem cells, maintain the ability to self-renew or differentiate. From the time of their specification during neural induction and throughout the building of the nervous system, neural progenitor cells preserve their broad developmental potential and replicative capacity to be able to produce the vast array of neuronal and glial cell types of the mature nervous system as, and when, required. Recently, considerable attention has been focused on identifying the molecular mechanisms responsible for maintaining neural progenitor or stem cell fate throughout ontogeny. The expression of a subset of SOX transcription factors is initiated concomitant with the acquisition of neural progenitor identity and is then maintained in the entire progenitor population of the developing and adult nervous system. Strikingly, studies in the central and peripheral nervous system of chick and mouse have revealed that SOX factors are key regulators of neural progenitor identity, promoting self-renewal in a context-dependent manner by sustaining the undifferentiated state of progenitor cells and maintaining their ability to either proliferate or differentiate.