During the last 35 years, accusations have been made that various nations and terrorists have employed biological, chemical, and toxin weapons in international warfare, internal conflicts, or terrorist operations. Most prominently, in the 1980s the UN found conclusive evidence that Iraq has used chemical weapons against Iran and, eventually, Iran answered in kind. Twenty-seven years later, Syria used chemical weapons against insurgents and civilians. Returning to Iraq, in addition to its chemical weapons, Iraq had a sizeable biological weapons program; and the Soviet Union secretly instituted the world’s largest and most sophisticated biological warfare program before its dissolution in late 1991. As for terrorism, the Aum Shinrikyo developed and used both biological and chemical weapons during 1991-1995; while scientist Bruce Ivens appears to have sent envelopes containing Bacillus anthracis spores to various public figures during September-October 2001; and the al Qaeda leadership has made clear that it seeks to acquire all types of weapons of mass destruction. In view of these developments, security experts active in the international arena ought to be familiar with the health and environmental effects of these weapons, circumstances which favor their use, the international laws that seek to prevent these weapons from being used and, when laws fail, how to determine whether one of these three weapon systems has indeed been used and the appropriate response to their use.