The Space Shuttle Environmental Control and Life Support System (ECLSS) provides the hardware and systems necessary to support manned space flight. ECLSS contains subsystems to: 1) provide active thermal control of systems throughout the vehicle, 2) maintain a habitable environment in the crew module, and 3) provide basic life support functions for the crew. Many of the unique concerns involving manned space flight have been addressed and resolved using creative engineering solutions, both for flight hardware and ground processing.The Kennedy Space Center (KSC) has processed and launched 66 Shuttle missions through 1994. Ground processing of ECLSS subsystems for flight creates its own unique set of concerns and challenges which must be addressed and resolved on a daily basis. With each successive Shuttle flight the Program has attempted to enhance ground processing to ensure that flight hardware can safely support mission objectives with reduced cost. This paper describes in detail the ground processing flow of the Space Shuttle ECLSS at KSC, which includes the testing and servicing required to ensure a vehicle is satisfactorily prepared to support the next mission. Particular emphasis is given to the various challenges experienced in the testing of Space Shuttle hardware on the ground.