It is nearly 15 years since biological weapons (BW) have become a significant national security preoccupation. This occurred primarily due to circumstances occurring within a short span of years. First was the official U.S. Government suggestion that proliferation of offensive BW programs among states and even terrorist groups was an increasing trend; second was the discovery, between 1989 and 1992, that the Union USSR had violated the Biological Weapons Convention (BWC) since its ratification in 1975 by building a massive covert biological weapons program; third was the corroboration by the UN Special Commission in 1995 that Iraq had maintained a covert biological weapons program since 1974, and had produced and stockpiled large quantities of agents and delivery systems between 1988 and 1991; and, fourth was the discovery, also in 1995, that the Japanese Aum Shinrikyo group, which had carried out the nerve gas attack in the Tokyo subway system, also had spent 4 years attempting—albeit unsuccessfully—to produce and disperse two pathogenic biological agents. The distribution of professionally prepared anthrax spores through the U.S. postal system in the weeks afterwards September 11, 2001, magnified previous concerns by orders of magnitude. In December 2002, after U.S. forces had overrun much of the territory of Afghanistan, it was discovered that the al-Qaida organization also had spent several years trying to obtain the knowledge and means to produce biological agents. These new factors shifted the context in which BW was considered almost entirely to "bioterrorism." Within 4 years, almost $30 billion in federal expenditure was appropriated to counter the anticipated threat. This response took place in the absence of virtually any threat analysis. The purpose of this monograph is to begin to fill that gap.