This chapter reviews the United States’ huge air transportation system as a complex socio-technical system of moderately linked organizations shaped by the country’s political culture. United States air traffic system providing both air navigation and traffic separation became a nationwide governmental service in 1936 after two decades of expanding private and public activity. By 1940, an embryonic operational air traffic management system was nearly in place and its essential, persisting dynamics established. The air traffic system is based as much on the cooperation of large cadres of pilots, air controllers, and airways facilities providers as on the array of sophisticated electronic, communications and computer technologies they operate. The central developmental dynamics swirl around the need to manage a growing volume of complex air traffic while anticipating and implementing the technical transformations necessary to keep safely ahead of demand for air traffic services.