This article examines the implications of emerging technological change on the multiplicity of future threats. Specifically, it examines the relevance of deterrence theory to both existing and new threats, some of which may surpass nuclear weapons in the risk they pose to the United States and humankind. It assumes science and technology growth will continue and will drive proliferation of advanced and potentially dangerous technologies. Rapid advances in biotechnology, nanotechnology, and directed energy may prove to be particularly dangerous. Deterring threats posed by nations, groups, and individuals will require new thinking regarding the application of deterrence theory particularly deterrence by denial. The article concludes that groups and individuals will continue to gain access to new capabilities and technologies that once were considered the exclusive domain of nation-states. These technologies will enable group and individual adversaries to overcome the tyranny of distance and make it easier to discover, act, surprise, and target almost any place on Earth. Individuals will be more difficult than groups or nation-states to track, but the greatest likelihood of catastrophic attack is likely to be posed by groups. If the United States can ensure adversaries will be precisely attributed through greater system transparency and immunization, attacks may be deterred.