This monograph reviews the history of biological warfare (BW) from prehistory to the present. It covers what we know about the practice of BW and briefly describes the programs that developed BW weapons based on the best available research. To the extent possible, it primarily draws on the work of historians who used primary sources, relying where possible on studies specifically focused on BW. By broadening our knowledge of BW, such studies have enabled us to write about the topic with more accuracy and detail than could have been done even a few years ago. This is an overview, not a defnitive history. Much about BW remains unknown, either because it is unknowable (due in some cases to the deliberate destruction of records) or because it is knowable only to some people (such as those who might have access to classified information) or because of the absence of academic research. This survey breaks the history of BW into three periods. The first section examines prehistory to 1900-the period before scientific advances proved that microorganisms were the cause of many diseases. The second section looks at the years from 1900 through 1945. This period saw the emergence of state BW programs, the employment of biological weapons in both world wars, and the use of biological agents by nonstate actors, including criminals. This period witnessed the most significant resort to BW. It included the first organized state campaign to wage BW-sabotage operations organized by the German government during World War I. It also saw the most extensive use-the Japanese attacks in China. Almost all the known victims of BW were Chinese, mostly civilians, who were killed in these operations. This period also saw the initial efforts to control BW in the 1925 Geneva Protocol, which essentially prohibited the first use of BW agents. Finally, the third section, covering the period from 1945 to the present, focuses mostly on developments during the Cold War, including descriptions of state BW programs as well as known uses of biological agents by states, terrorists, and criminals. This history focuses on those agents covered by the BWC, which prohibited weapons disseminating biological agents or toxins. Biological agents are replicating biological entities, such as bacteria. Toxins, poisons of biological origin, are similar to chemical warfare agents and also have been banned by the Chemical Weapons Convention.