have become one of the key security issues of the twenty-arst century.1 Three factors that arst emerged in the 1990s have contributed to this phenomenon. First, revelations regarding the size, scope, and sophistication of the Soviet and Iraqi biological warfare programs focused renewed attention on the proliferation of these weapons.2 Second, the catastrophic terrorist attacks on September 11, 2001, and the anthrax letters sent to media outlets and Senate ofaces in the United States during the following month, demonstrated the desire of terrorists to cause massive casualties and heightened concern over their ability to employ biological weapons.3 Third, signiacant advances in the life sciences have increased concerns about how the biotechnology revolution could be exploited to develop new or improved biological weapons.4 These trends suggest that there is a greater need than ever to answer several fundamental questions about biological warfare: What is the nature of the threat? What are the potential strategic consequences of the proliferation of biological weapons? How ef-