This is an introduction to a special issue of the journal Restorative Neurology and Neuroscience which contains a series of papers presented at a satellite symposium held in conjunction with the European Forum of Neuroscience, Berlin, July 1-2, 1998, entitled "Visual System Damage: Residual Vision and Plasticity". The symposium highlighted research findings both from animals and humans which sustained brain injury in early development and in adulthood. The findings demonstrate the degree of residual vision the injured brain possesses and summarize the effects of drugs and training on the plasticity of the visual system. As this conference demonstrated, the visual system is able to respond in many ways in an adaptive manner to lesions inflicted early in life and in adulthood. These changes may bring about spontaneous recovery of visual functions as long as the brain contains a sufficient capacity of residual vision. Both in children and in adults, systematic visual training can help patients to regain some visual functions which have previously been considered to be irrevocably lost. By carefully assessing residual vision it is proposed that the potential for plasticity of the visual system can be utilized to achieve clinical improvement using appropriate training paradigms.