This report surveys the debate over the requirements for a new congressional authorization for the use of military force (AUMF). It captures the results of two workshops, an extensive literature review, and consultations with senior experts and practitioners in the executive branch and Congress. The first of the two RAND-organized workshops, in November 2014, brought together experts on the global threat environment to examine the evolution of the terrorist threat and its likely trajectory. The second, in February 2015, elicited the perspectives of legal and policy experts, focusing on specific elements of notional versionsof a congressional AUMF. We thus sought to survey the current thinking among both terrorism and legal experts to gauge the spectrum of views on the subject, ascertain the most important elements of such an authorization, and, by adding our own insights on counterterrorism operations and the threat trajectory, offer options to help inform the congressional debate on an AUMF. In doing so, we were cognizant that the debate was shifting and that congressional supportfor a new AUMF was fluctuating. In the midst of our effort, the White House submitted to Congress its own draft authorizationessentially providing a specific proposal to test against the theoretical models constructed for this study but also rendering the subject even more politically charged than in the past. We remain mindful of these political realities while also presenting an objective, nonpartisan view of possible directions and implications for an AUMF from a broad nationalsecurity perspective.