Nestin was originally identified as a neuronal stem cell marker during central nervous system (CNS) development. It belongs to an intermediate filament protein family, and it is the most widely used marker for identifying neuronal stem cells. Nestin is required for survival, renewal, and mitogen-stimulated proliferation of neural progenitor cells. However, the exact function of nestin is not very clear. Nestin is involved in structural organization of the cells through assembling into heterodimers with vimentin or alpha-internexin in a phosphorylation-dependent process to form intermediate filaments. The expression of nestin is downregulated and replaced by expression of the neurofilament proteins upon neural differentiation/maturation.Expression of nestin has also been reported in non-neuronal immature or progenitor cells such as pancreatic islet progenitor cells, angiogenic endothelial cells, glioma cells, and bone marrow mesenchymal stem cells. Recent studies also showed that nestin expression can be detected in repair processes in the CNS and in various tumor cells. Thus, it has been used as a cancer stem cell marker. The usage of nestin as a novel prognostic indicator and possible target for tumor anigogenesis has been also proposed.