Since the pioneering studies of Ramon y Cajal the inability of lesioned adult CNS axons to regenerate has been well established. During the past years advancements in molecular, cellular and biochemical knowledge have provided new insights into the extrinsic mechanims underlying regeneration failure. The rapid progress in this field has already led to the development of new concepts for therapeutic manipulations. This book provides a comprehensive overview of structural and molecular changes induced by an invasive CNS lesion and their involvements in regeneration processes. Moreover, it demonstrates the strong growth-promoting actitivies of implanted glial cells. The data is discussed in relation to current knowledge on the mechanisms of axonal degeneration and regeneration and in terms of their relevance for the development of novel therapeutic strategies.