Ariel IIIcarries equipment from five scientific groups in the U.K. to measure ionospheric and high atmosphere properties. The project management structure is described.The spacecraft configuration evolved from two fundamental requirements—spin stabilization and power supply by solar cells. The evolution of the structure and sub-systems, together with the operation of various mechanisms, is outlined. The reliability, needed and achieved, of electronic ground equipment is stressed, and operations at the Western Test Range are discussed.The choice of orbit was a compromise between several experimental requirements and the capability of theScoutlaunch vehicle. Data acquisition and processing are discussed.