This chapter discusses the evolution of air traffic control (ATC) and management automation. Terminal control areas came into being; within these areas, generally shaped like an inverted wedding cake, all traffic, whether flying under visual or instrument flight rules, was required to submit to positive control by terminal area controllers. En route air traffic control began to be utilized in 1935 along airways marked by aeronautical beacon lights. The introduction of interrogation devices, the Air Traffic Control Radar Beacon System at radar sites, and transponders in aircraft that responded to queries from the interrogators made possible secondary surveillance radar systems. System Command Center personnel act as coordinators between users of the airspace and controllers in the various ATC facilities. The air traffic control system found itself handling considerable peak loads of traffic with outdated equipment, chronic understaffing, and less experienced controllers in many facilities.