In the past decades, the public has been forced to revise its perception of the apparent triumph of modern hygiene and medical microbiology over infectious diseases. Not only have older infections reemerged but new epidemics, like AIDS, have lead to public uncertainty. With the onset of the bovine spongiform encephalopathy epidemic in Great Britain, novel infectious agents came into the public spotlight, ones that do not cause classical inflammation but a slow and irreversible degeneration of the central nervous system. Sensational from a scientific point of view, these agents, called proteinaceous infectious organisms or prions, were shown to be self-replicating without nucleic acid sequences to encode genomic information. In this volume, leading scientists deal with the medical, scientific and public health questions that prion infections raise.