The targeted delivery of genes and the transplantation of suitable cell types into the adult nervous system have received considerable interest over the last years. The development of improved vector systems for in vivo gene delivery and the discovery of neural stem cells in the adult nervous system have opened new venues for potential therapeutic intervention in progressive neurodegenerative disease and nervous system injury. Thus, strategies have evolved for the delivery of potentially neuroprotective molecules, such as neurotrophic factors, and the replacement of cells and tissue lost due to CNS injury and degeneration.