Recent proliferation surprises in the Middle East-the failure to find weapons of mass destruction (WMD) in Iraq, Libya's decision to eliminate its WMD, and evidence of significant progress by Iran toward a nuclear weapons capability-underscore the need for the nonproliferation community to reassess some of its key assumptions about WMD proliferation and the nature of the evolving international landscape. Such a reassessment must be highly speculative. Much about Iraq's WMD programs is likely to remain a mystery due to the destruction of records and the looting of facilities following the fall of Baghdad, as well as the continuing silence of many Iraqi weapons scientists and former government officials.1 Likewise, the calculations driving key proliferation-related decisions by Libya and Iran remain murky. This lack of knowledge, however, should not inhibit attempts to grasp the implications of these developments for U.S. nonproliferation and counterproliferation policy. Although this paper focuses primarily on Iraq, it also seeks to draw lessons from recent experiences in Libya and Iran to understand better how proliferators think about WMD; the challenges in assessing the status and sophistication of developing world WMD programs; the contours of the emerging international proliferation landscape; and the efficacy of various policy instruments available to the United States for dealing with these so-called ultimate weapons.