Propulsion and power requirements for unmanned air vehicles (UAV) vary from 10-100's milliwatts for micro-UAV's to 10-100's kilowatts for telecommunications, reconnaissance/combat UAV's. Electrochemical fuel cells are highly efficient, modular, rechargeable, and minimal vibrations/torque electrical power sources for any size power system. Due to these inherent attractive fuel cell attributes, lightweight fuel cells that minimize fuel cell stack and accessory weight are being developed for electric vehicle, man-portable, and micro and regenerative UAV applications. Regenerative fuel cells are baselined for future high altitude telecommunications platforms such as Helios and Sky Station. With future improvements in electric vehicle fuel cell technology anticipated, fuel cell usage on air-breathing UAV's is also expected.