Nuclear explosives are no longer beyond the reach of terrorists. The Wild Atom-- a two-day simulation of a nuclear terrorist threat against the United States--demonstrated that, because interdiction is difficult, governments must combat illicit possession of nuclear weapons, improve working relationships among domestic agencies, and curb rivalries among national and international counterproliferation and counterterrorism officials. If a nuclear incident occurs, officials must be trained for consequence management. And the national security community and national disaster medical community must be practiced in working together and with experts in other countries. This report offers a chilling glimpse into the complexities of dealing with the threat of nuclear terrorism.