Prion diseases are incurable neurodegenerative conditions affecting both animals and humans. They may be sporadic, infectious, or inherited in origin. Human prion diseases include Creutzfeldt-Jakob desease (CJD), Gerstmann-Straussler-Scheinker disease, kuru, and fatal familial insomnia. The appearance of variant CJD, and the demonstration that is caused by strains indistinguishable from bovine spongiform encephalopathy (BSE) in cattle, has led to the threat of a major epidemic of human prion disease in the UK and other countries where widespread dietary exposure to bovine prions has occurred. This article reviews the history and epidemiology of these diseases, and then focuses on important areas of current research in human prion disorders.