A paper on U.S. counterterrorism measures notes that the September 11 attack is bringing fundamental changes in national security policy and nonproliferation policy. U.S. national security policy will be motivated primarily by homeland defense. The overall goal is the defense of the American homeland, the prevention of future attacks, and the use of diplomatic and military means to make sure that the American people are as safe as possible. A second paper on U.S. national security presents an overview of the current status of nuclear terrorism and its threat to the United States. Three papers focus on nonproliferation regimes and proliferation technologies, with attention to arms control for anthrax, implications of the war against terrorism for regimes under the Treaty on the Non-Proliferation of Nuclear Weapons, and the regulation of scientific research of potential relevance to biological warfare. Two papers relevant to Middle East security consider the implications of September 11 for Middle East security, as well as Iran's strategic environment after September 11. Two papers consider the importance of adherence to nonproliferation among the nations of South Asia; and three papers consider the significance of major-power relations and nonproliferation under the impact of September 11. The concluding paper discusses the assessment of risk for terrorist acts of mass destruction and the crafting of responses.