The main cause of disability following spinal injury is failure of axons to regenerate and reconnect the spinal cord with the brain. If patients with cord lesions are ever to make a full recovery some means will have to be found to restore ascending sensory and descending motor connections. Until the last few years there has been a very limited understanding of the reasons why axons in the central nervous system (CNS) fail to regenerate, but as a result of recent work the picture is now much clearer.