The development of a functional nervous system critically depends on the production of a diverse array of neuronal and glial cell types at the correct locations, at the right time and in appropriate numbers. This cellular diversity arises through a coordinated series of steps that regulate neural progenitor differentiation, identity specification, axonal outgrowth and synapse formation. We have employed developmental genetics to characterize and manipulate specific neuronal populations in the spinal cord that serve dedicated roles in sensory and motor circuits. Our recent work has delineated the transcriptional program that drives late neurogenesis in the spinal cord and specifies sensory cerebrospinal fluid-contacting neurons during embryonic stages previously thought to be exclusively gliogenic. We have also investigated the ontogenetic mechanisms underlying astrocyte heterogeneity and provided strong evidence for the existence of region-specific astrocytic subtypes whose allocation depends on progenitor identity.