The U.S. needs an agile, proactive approach to anticipating, deterring, and defeating threats from explosive attacks by terrorists. Since the explosive attacks in London in July 2005, Sandia has been actively engaged in providing scientific understanding to Transportation Safety Administration (TSA) decision makers. Examples of our work include evaluating the feasibility of creating explosives from commercially available pre-cursors, characterizing liquid explosives using both experimental and computational approaches, and developing and evaluating detectors for this new class of explosive mixtures. These activities have used interdisciplinary approaches, test capabilities, and modeling and computation to provide technically solid and time-critical results.