This monograph is one of those rare scientific books that not only do not lose their significance several years after publication, but, on the contrary, are becoming increasingly in demand. The success of its first edition (2000) is based on the author's proposed explanations for the reasons for the return, spread and disappearance of a number of pandemic diseases, in particular smallpox and AIDS, which significantly fill the gaps in understanding about these processes. The need to reissue the book is due to the continuing deterioration of the global epidemic situation as a whole, the intensification of smallpox infections, as well as the lack of any success in combating the HIV/AIDS pandemic. According to the author, there is a need for a serious rethinking of many epidemiological views of the 20th century as inconsistent with the real state of affairs. In addition, the monograph, for the first time in Russian literature, thoroughly covers the epidemiology of a biological terrorist act and the methodology for identifying such a crime. The book is well illustrated, contains appendices and is intended for a wide range of specialists.