The Shuttle Extravehicular Mobility Unit (EMU) is an integral component in successful satellite salvaging operations. FMU evolution to its current operational status has occurred through implementation of carefully analyzed and thoroughly tested changes. The net result of these changes is known as the Block II FMU. This paper discusses the basic FMU system requirements, the philosophy used in the design of the Block I EMU, and the operation of the Life Support System (LSS); outlines the evolution of the Block II configuration; and briefly discusses future progression of the LSS. The Block II LSS configuration has improved serviceability between flights, simplified user operation, improved performance, decreased maintenance (by extending component life), and, most importantly, improved mean time between failures by a factor of fourteen.