Air traffic control (
ATC) is a service provided by ground-based
controllers who direct
aircraft on the ground and through controlled
airspace, and can provide advisory services to aircraft in non-controlled airspace. The primary purpose of ATC worldwide is to prevent collisions, organize and expedite the flow of air traffic, and provide information and other support for
pilots. In some countries, ATC plays a security or defensive role, or is operated by the military.