After initial skepticism, it's now generally accepted that prions exist, that they differ from all other pathogens, and that they are infectious in several species. Prions are implicated in spongiform encephalopathies such as kuru, Creutzfeldt-Jakob disease and fatal familial insomnia in humans, scrapie in sheep, and a bovine encephalopathy that may be transmissible to humans. Driven by prions' novelty and by concern about their public health effects, awareness of these pathogens has grown enormously in recent years, prompting an immense amount of sometimes conflicting research. This definitive account of prion biology and disease was assembled to provide investigators with reliable reference material, young scientists with encouragement to explore the field, and educators with information on a topic that has captured the imagination of students at every level. The most authoritative and up-to-date source of knowledge yet published on this unique form of pathogen, the book has been written by Stanley Prusiner, winner of a 1997 Nobel Prize for his discovery of prions, and a group of internationally recognized experts on prions' biology and pathogenic effects.