Anthrax is primarily a disease of herbivores. Humans almost invariably contract the natural disease directly or indirectly from animals or animal products. Anthrax essentially ceased to be regarded as a disease of major health or economic importance after the enormous successes of Max Sterne’s veterinary vaccine developed in the 1930s, and subsequent analogs in the former Soviet Union, in dramatically reducing the incidence of the disease in livestock throughout the world in the ensuing two decades. This fourth edition of the anthrax guidelines encompasses a systematic review of the extensive new scientific literature and relevant publications up to end 2007 including all the new information that emerged in the 3–4 years after the anthrax letter events.