Stem cells hold great promise for therapeutic repair after spinal cord injury (SCI). This review compares the current experimental approaches taken towards a stem cell–based therapy for SCI. It critically evaluates stem cell sources, injury paradigms, and functional measurements applied to detect behavioral changes after transplantation into the spinal cord. Many of the documented improvements do not exclusively depend on lineage-specific cellular differentiation. In most of the studies, the functional tests used cannot unequivocally demonstrate how differentiation of the transplanted cells contributes to the observed effects. Standardized cell isolation and transplantation protocols could facilitate the assessment of the true contribution of various experimental parameters on recovery. We conclude that at present embryonic stem (ES)–derived cells hold the most promise for therapeutic utility, but that non-neural cells may ultimately be optimal if the mechanism of possible transdifferentiation can be elucidated.