As deputy assistant secretary for research, development, and simulation in the US Department of Energy Office of Defense Programs, Gil Weigand provides programmatic and policy direction for the DoE's nuclear weapons research, development, and simulation work. In partnership with the national labs, he leads the effort to preserve the technology base and develop programs for the surety, reliability, military effectiveness, and credibility of the nation's nuclear-weapons stockpile.Prior to this job, Weigand was deputy assistant secretary for strategic computing and simulation and a senior information officer for the DoE Office of Defense Programs, where he led advanced initiatives in high-performance computer simulation, computation, and communications. In particular, he was responsible for directing the Accelerated Strategic Computing Initiative, which has created leading-edge computational modeling and simulation tools necessary to move from test-based to simulation-based assessment and certification. The ASCI initiative is based on the Comprehensive Test Ban Treaty, an international treaty to move toward no nuclear testing announced by President Bill Clinton on 11 August 1995.Paul Messina now manages ASCI as DoE deputy assistant secretary for advanced simulation and computing for defense programs. He is on a two-year leave from the California Institute of Technology, where he is assistant vice president for scientific computing, a faculty associate in scientific computing, and director of the Center for Advanced Computing Research. He has a joint appointment at the Jet Propulsion Laboratory as manager of high-performance computing. Messina is also on leave from the position of chief architect for the National Partnership for Advanced Computational Infrastructure, where he established and led the Scalable I/O Initiative.Editor-in-chief George Cybenko recently talked to Weigand and Messina about their roles in ASCI and the Alliance Program, and their thoughts about where the high end of computational performance is headed.