The North Atlantic Treaty Organization's nuclear forces were central to deterrence and defence during the Cold War. Their future role is far less clear in the dramatically changed security environment since its end. Despite concerns about the long-term evolution of Russia and China, the major threats to national and international security today stem not from confrontations between great powers, but from proliferation and terrorism.Proliferation concerns include Iran's suspicious and extensive weapons of mass destruction programs, especially its nuclear and missile activities. The discovery of the large enrichment facility at Natanz as well as other clandestine activities revealed two decades of Iranian noncompliance with its international obligations. North Korea's nuclear test and its diplomatic brinkmanship highlight the increasing dangers of its longstanding nuclear and missile programs and the difficulties of disarming the regime.The growing reality of cooperation among proliferant states is troubling. The weapons of mass destruction and missile cooperation between North Korea, Pakistan, and Iran have been examined in the open literature. The question is whether that cooperation was limited to these and a few other states, or provides a blueprint for the future. Clearly, there are a growing number of states that now possess or are developing WMD- and missile-related technological capabilities and expertise. Will these capabilities be shared, and under, what, if any, constraints? Will they wind up in black markets? All of these activities undermine regional stability and threaten US and NATO security, and could lead to proliferation cascades and regional arms races. There is a second tier of states that might consider nuclear or other weapons of mass destruction in the future, including Ukraine, Kazakhstan, Nigeria, Egypt, Turkey, Saudi Arabia, South Korea, Japan, and Indonesia.The potentially catastrophic nexus between rogue regime behaviour and terrorist tactics is also a grave concern. The active pursuit of nuclear and other weapons of mass destruction materials and technologies by terrorists and so-called rogue states has been abetted both by other proliferant states and by nonstate networks such as the A. Q. Khan operation. The risks to national and international security are compounded as peaceful pursuits of nuclear energy increase the traffic in nuclear materials and technology.In response, the United States and NATO member states have advocated collaborative efforts to combat terrorism and to strengthen the nonproliferation regime while ensuring access to the advantages of nuclear energy. Multilateral counterterrorism initiatives include the global initiative to combat nuclear terrorism. Efforts to strengthen and enforce nonproliferation norms are being reinvigorated through multilateral programs such as the proliferation security initiative and through efforts to gain universal adherence to the additional protocol to International Atomic Energy Agency safeguards agreements. The United States is currently pursuing a nuclear energy partnership that would both encourage growth of domestic nuclear energy use and promote international arrangements to restrict access to fuel cycle technologies by additional states.International non- and counterproliferation, along with counterterrorism, efforts such as these are critical. However, they are not enough by themselves to protect US and NATO security interests, or to resolve problems. The complex geopolitics ofthe emerging security environment, where issues of WMD proliferation and nuclear weapon policy intersect, demands a clear and credible security strategy that addresses US and NATO security objectives in multiple areas. These include ensuring confidence in the safety, security, reliability, and sustainability of the US nuclear-weapon stockpile and its supporting infrastructure; dealing responsibly with all weapon-usable materials, both nationally and globally; and meeting all international security commitments. …