The book is devoted to an urgent problem of a scientific, medical, social and political nature - the problem of the so-called prion diseases, which gained universal fame at the very end of the 20th century. This is a fascinating story about the history of scientific searches and discoveries. The value of the book is that it covers the problem of prion diseases in general and in its most intriguing details. In it you can find materials about the historical origins and modern sources of this newly-minted "Evil," learn about today's measures of protection against prion diseases, get acquainted with the threats of their spread, as well as with the possibility of defeating them in an uncertain future. The book successfully combines the popularity of presentation and scientific reliability, and therefore can be in demand both in the scientific environment and among the general public, as well as in the study of special disciplines (medicine, biology, veterinary medicine, food technology, etc.).