Natural outbreaks of transboundary infectious diseases and pandemics are global threats posing international challenges of medical, veterinary, social, and economic character. These diseases have their specific sources and are driven by a range of factors and mechanisms that ensure their transboundary spread. The main driver of transnational spread of infectious diseases is human activity that violates and distorts ecological and climate balance. This disbalance leads to emergence of new pathogens and to expansion of geographical areas of already known diseases and of the range of their host organisms that increasingly include humans. Understanding these aspects is critical for countering existing and future outbreaks of transboundary infections. There is also a risk that infectious potential of microorganisms may be used by armed actors, including parties to politicalmilitary conflicts and terrorists, for their own purposes. While emergence and spread of transboundary infections give rise to a number of problems that reduce the effectiveness of measures for preventing and eliminating them, adequate knowledge about transboundary infections makes it possible to develop a strategy for the management of such diseases at the international level.