The symposium was held on 13-14 May 2015 at NDU, Fort Lesley J. McNair, Washington, D.C. This year's symposium examined whether and how current assumptions about the WMD threat and response changed in light of recent experience, changes in the security environment, and the spread of technology. Participants and speakers explored developments such as Syria’s chemical weapons use and disarmament, the outbreak of Ebola and the U.S. response, nuclear negotiations with Iran, Russia’s actions in Ukraine, and North Korea’s continuing effort to build nuclear weapons, to identify their implications and lessons for the future of countering WMD. Leading policymakers, practitioners, and experts shared their views on these important topics.