A major new facility was required to meet the contamination control requirements of the Hubble Space Telescope (HST) Program during the Assembly and Verification phase of the program. The Vertical Assembly and Test Area (VATA) facility would have to maintain a volumetric cleanliness level of better than 10,000 for all operations of assembly and verification testing of the HST. The assembly of this 43 foot long by 14 foot and 10 foot diameter telescope of 25,000 pounds was expected to require access for 30 to 50 people at a time and would be conducted with all major subassemblies being retained in a vertical attitude. This resulted in the need for a building with an inside height of ninety (90) feet, and 20 ton bridgecrane with a hook height of seventy-six (76) feet and a Vertical Assembly Test Stand (VATS) of five stories (platform levels). It was decided that, to provide the most effective clean room environment, a horizontal flow system would be required. The room had to be long enough also so that incoming equipment and hardware could enter the opposite end of the room (downstream of the HST) without degrading the assembly and test area. The facility (55 ft. wide by 90 ft. high by 120 ft. long) incorporated a fifty-five (55) foot wide by ninety (90) foot high High Efficiency Particulate Air (HEPA) filter wall (non-DOP tested), a pre-filter system, a downstream balance chamber system to divert the air through an overhead return cavity and back through the filter system and a separately filtered makeup air system (also used for cooling purposes on the HST during testing). Lockheed Missiles and Space Co., Inc. developed this facility, in Sunnyvale, California for the HST Program and its operation has met and exceeded all requirements in maintaining the strenuous cleanliness levels needed for the HST assembly and verification testing. This paper will discuss the requirements and the development of this facility.