Prion diseases, or transmissible spongiform encephalopathies, include Creutzfeldt-Jakob disease (CJD) in humans and scrapie and bovine spongiform encephalopathy (BSE) in animals. These neurodegenerative diseases are invariably fatal and can be transmitted by inoculation or dietary exposure. They are associated with the accumulation of an altered, disease-associated form of the normal prion protein. Pathologically, prion diseases result in neuronal cell death and a characteristic spongiform appearance of the brain tissue. The emergence of a variant form of CJD (vCJD) in the United Kingdom in 1996 has been causally and experimentally linked to the UK BSE epidemic in the 1980s and early 1990s. The finding that BSE is transmissible to different animal species, unlike previously characterized prion diseases such as sheep scrapie, has raised enormous public health concerns worldwide. Although it is not yet possible to gauge the size of a potential vCJD epidemic, preliminary data indicate a significant dietary exposure to BSE-infected material in Britain and wider implications of the transmissibility of prion diseases. The threat to public health has intensified research efforts to understand the molecular basis of prion diseases, understand their transmission between species, improve methods of diagnosis, and develop therapeutic strategies for treatment and prevention of disease. In this review, we summarize current data on the pathology of BSE and vCJD and the epidemiology of vCJD, and we outline public health implications based on these data, emphasizing preventative measures and areas of research for screening and diagnosis.