1. Transmissible Spongiform Encephalopathies: The Viral Concept and an Application2. The Prion Theory: Background and Basic Information3. [URE3] and [PSI]: Prions of Saccharomyces cerevisiae4. Structural Biology of Prions5. Strain Variations and Species Barriers6. Resistance of Transmissible Spongiform Encephalopathy Agents to Decontamination7. Human Prion Diseases: Cause, Clinical and Diagnostic Aspects8. Epidemiology and Risk Factors of Transmissible Spongiform Encephalopathies in Man9. Bovine Spongiform Encephalopathy and Its Relationship to the New Variant Form of Creutzfeldt-Jakob Disease10. Animal Transmissible Spongiform Encephalopathy: Clinical and Diagnostic Aspects11. The Challenge for the Public Health System