In January-February 2005, the National Academies Committee on Counterterrorism Challenges for Russia and the United States and the Russian Academy of Sciences Standing Committee on Counterterrorism held a workshop on urban terrorism in Washington, D.C. Prior to the workshop, three working groups convened to focus on the topics of energy systems vulnerabilities, transportation systems vulnerabilities, and cyberterrorism issues. The working groups met with local experts and first responders, prepared reports, and presented their findings at the workshop. Other workshop papers focused on various organizations’ integrated response to acts of urban terrorism, recent acts of terrorism, radiological terrorism, biological terrorism, cyberterrorism, and the roots of terrorism.