The United Nations has defined biological warfare as the use of any living organisms (e.g. bacteria) or infective material derived from them, in order to cause disease or death in humans, animals, or plants. The effectiveness of these organisms depends on their ability to multiply in the person, animal or plant attacked.

While the United Nations is a post-World War II institution, biological warfare is considerably older. Biological weapons have been used throughout world history: crops and livestock have been destroyed, water supplies have been contaminated, and humans have been exposed to lethal diseases.

Some historians have suggested that the second plague pandemic in the Middle Ages was a result of a rather crude form of biological warfare. During the fourteenth century, the city of Kaffa, or Caffa (now Feodosiya, Ukraine), was under siege by Tatars, whose own population was suffering from an outbreak of...