Neural stem cells (NSCs) are potentially attractive cell sources for repair of injured spinal cord circuits. They can be derived from embryonic central nervous system tissue, pluripotent stem cells, induced pluripotent stem cells, or trans-differentiated cells. Recent studies demonstrate that NSCs or neural progenitor cells (NPCs) can survive grafting into sites of severe spinal cord injury (SCI), differentiate into neurons and glia, and extend very large numbers of axons over substantial distances for connectivity with host neurons below sites of injury. Reciprocally, host axons regenerate into the NSC/NPC grafts and form synaptic connections with graft-derived neurons. Therefore, NSC/NPC graft-derived neurons serve as neuronal relays that re-establish neural transmission across the lesion site, improving functional outcomes even after severe SCI. These findings are confirmed in the larger primate system, paving a translational path for clinical application.