For many decades, the inability of lesioned central neurons to regrow was accepted almost as a "law of nature", and on the clinical level, spinal cord and brain lesions were seen as being irreversible. Today we are starting to understand the mechanisms of neuronal regeneration in the central nervous system and its presence in the periphery. There is now a rapid expansion in this field of neuroscience. Developmental neurobiology has produced tools and concepts that start to show their impact on regeneration research. This is particularly true for the availability of antibodies and factors and for the rapidly growing cellular and molecular understanding of crucial aspects of neurite growth, guidance, target finding, and synapse stabilization. New cell biological concepts on the mechanisms of neuron survival and death and on the interaction of inflammatory cells with the central nervous system also find their way into the field of spinal cord and brain lesions and have, indeed, led already to new therapeutic approaches. This review briefly summarizes the current knowledge on the mechanisms involved in degeneration and tissue loss and in axonal regeneration subsequent to spinal cord lesions, particularly in mammals and humans.