Viral infections of the nervous system are important because they are associated with high morbidity and mortality. A variety of pathogenetic mechanisms are involved in these infections and an understanding of the pathogenesis is essential in understanding the diagnostic and clinical management aspects of the disease. Specialized investigations are often necessary for definitive diagnosis, although a presumptive diagnosis should often be suspected on the basis of the clinical features. Many of the chapters in this book are written by neurologists who are experts in basic science research of their topic in addition to active clinical practice in their specialty.