The development of a fuel cell energy storage system (FCESS) for the Extravehicular Mobility Unit (EMU) carried out by Ergenics Power Systems, Inc. (EPSI) under NASA contract is now in its fourth year, The applicability of this promising technology for the EMU has been well established and its advantages for this and other aerospace applications are clearly apparent. The combination of excellent cycle life and shelf life, high gravimetric and volumetric energy density, and rapid rechargeability make this technology a cost effective and technically attractive choice. The program, initiated with a conceptual design, has progressed successfully through the breadboard stage. Presently, the technology is being refined through the design, fabrication and testing of a vacuum rated system. The current status of these tasks is summarized In the following text.