Critical infrastructure and its interdependencies play a vital role in our daily functions. Our economies, government, and way of life depend on the sound function of these integrated systems. Analysis of these systems, however, has historically been limited: system owners and operators have limited information outside their domain space (and that legal impediments often limit their ability to better understand the broader system), and very few entities have the desire to better understand these systems as a whole, let alone their interconnections. The National Infrastructure Simulation and Analysis Center (NISAC) is one such entity. NISAC, a program managed by the U.S. Department of Homeland Security (DHS) and comprised of a core partnership of Sandia National Laboratories (SNL) and Los Alamos National Laboratory (LANL), draws on years of modeling experience of various types, focused on infrastructure, population, and the economy, to examine questions pertinent to DHS regarding the function of economy and critical infrastructure of the United States (see Figure 1).