The various configurations being considered for Space Station Freedom have resulted in a moving target for tomorrow's demand for EVA and the requirements that will be imposed on the Extravehicular Mobility Unit (EMU). The Shuttle EMU is baselined to perform the assembly and operational activities of station and is currently undergoing the necessary incremental re-certification.This paper presents the evolution of an EMU from two perspectives. First, evolution is discussed within the context of continuously improving the life support system and the space suit assembly from the Mercury Program to NASA's current flight EMU. This includes a status of the on-going enhancements and a discussion on the merits of additional improvements. The second perspective describes evolution for future programs involving significant differences in mission requirements and environments.