This document summarizes prion diseases, which are a group of progressive neurodegenerative disorders known as transmissible spongiform encephalopathies. The diseases affect both animals like sheep and deer, as well as humans. They are caused by misfolded prion proteins that form plaques in the central nervous system, disrupting normal tissue structure and causing holes or vacuoles in neurons. Prion diseases have a long incubation period, cause neurologic symptoms, and are ultimately fatal. Key features include spongiosis, gliosis, and neuronal loss. The diseases can be sporadic, genetic, or acquired through infection or medical procedures.