Neural stem cells (NSCs) are an undifferentiated population of cells residing in the tissue lining the ventricular system of both the embryonic and adult mammalian central nervous system (CNS) (1 –3 ). When isolated under the appropriate genetic or epigenetic conditions, NSCs have the ability to self renew and produce clinical amounts of cells that may be well characterized in vitro and in vivo, cryopreserved, or ready for therapeutic use. Upon transplantation into the adult CNS, NSCs integrate seamlessly within the host tissue and differentiate according to the local microenvironment into any one of the principal CNS cell types (neurons, astrocytes, or oligodendrocytes). These attributes make NSCs a good source of cells for cell replacement therapy for neurological disorders. However, this source of neural tissue will not reach the clinical stage unless it is well characterized both in vitro and in animal models.