Two electromagnetic phenomena have the potential to create continental-scale disasters. The first, nuclear electromagnetic pulse (EMP), results from a nuclear detonation high above the tropopause. The second, a major solar storm, or "solar tsunami" occurs naturally when an intense wave of charged particles from the sun perturbs the earth's magnetic field. Both phenomena can debilitate electrical and electronic systems necessary for the operation of infrastructure systems and services. One reason why a U.S. protection program has yet to be initiated is that policy makers continue to wrestle with the question of where to begin, given the Department of Homeland Security’s list of 18 critical infrastructures. DHS is pursuing a "risk-based" prioritization approach in developing general protection programs. Such an approach is invaluable in developing an EMP/solar storm threat protection initiatives as well. A simple risk analysis indicates the electric power and information/communications infrastructures pose the highest risks relative to EMP and solar storm effects.