There is now evidence that irreversible brain damage accumulates very early in the course of multiple sclerosis. This book reviews the main neurobiological, magnetic resonance imaging, and clinical aspects of the early phases of the dis ease. Mechanisms ofirreversible axonal damage and the role played by the inter action of glia and the axon are highlighted. In contrast to what was believed for a long time, the sufficient availability of oligodendrocyte precursor cells to promote remyelination in acute lesions has now been demonstrated. For reasons not understood, this remyelination process...