This major new work contains reviews of recent and current research on prions and prion diseases. The focus is on the cellular, biochemical, and genetic aspects of this unusual group of neurodegenerative disorders, which was the subject of a recent Nobel Prize. The book is essential reading for all researchers working in the field and is recommended reading for scientists in other areas of biology and medicine. Contributions by internationally recognized experts cover a variety of experimental systems currently being used to understand the mechanisms underlying these fascinating and deadly diseases. The latest results and key theoretical issues are discussed, including the physical structure of prions, models of prion formation and pathogenesis, BSE and new variant Creutzfeldt-Jakob disease, yeast prions, and the strain phenomenon.