Large electromagnetic launchers require multigigawatt (GW) power levels and mega-ampere currents to be supplied at multikilovolts during the launch of a high-speed projectile. Power systems that operate under these conditions are not readily available and expert development is therefore needed to design, assemble, and operate them safely. The options available for energy storage and GW power delivery are discussed. Some of the larger systems that have been built are described and their features discussed.Index Terms-Electromagnetic (EM) launching power supplies, energy storage, pulsed power systems, railgun power supplies, railguns.