Airspace within which aircraft may be subject to air traffic control.

Just about all of the airspace in the United States. There are several categories. Continental Control Area: Covers all of the "lower 48" plus most of Alaska. Extends from 1,501 feet above the surface up to infinity, or the base of the PCA, the Positive Control Area. Control Zone: The area around an airport that has a control tower. Usually a 5 statute mile circle around the airport, and any extensions necessary for instrument approaches. It extends from the surface to the base of the Continental Control Area. Positive Control Area: The airspace extending from 18,000 feet MSL to Flight Level 600 (for all intents and purposes 60,000 feet). TCA: Terminal Control Area. Airspace around larger airports. VFR or IFR, you need permission to be in there.

Controlled airspace is an aviation term used to describe airspace in which traffic levels are such that it has been determined that air traffic control (ATC) must provide some form of separation between aircraft. It is the opposite of uncontrolled airspace.