A prohibited airspace is an area (volume) of airspace within which flight of aircraft is not allowed, usually due to security concerns. It is one of many types of special use airspace designations and is depicted on aeronautical charts with the letter "P" followed by a serial number. It differs from restricted airspace in that entry is typically forbidden at all times from all aircraft and is not subject to clearance from ATC or the airspace's controlling body.

According to the U.S. Federal Aviation Administration (FAA): "Prohibited areas contain airspace of defined dimensions identified by an area on the surface of the earth within which the flight of aircraft is prohibited. Such areas are established for security or other reasons associated with the national welfare. These areas are published in the Federal Register and are depicted on aeronautical charts."

Some prohibited airspace may be supplemented via NOTAMs. For example, Prohibited Area 40 (P-40) and Restricted Area 4009 (R4009) often have additional restricted airspace added via a NOTAM when the President of the United States visits Camp David in Maryland, while normally the airspace outside of P-40 and R4009 is not prohibited/restricted.

Violating prohibited airspace established for national security purposes may result in military interception and/or the possibility of an attack upon the violating aircraft, or if this is avoided then large fines and jail time are often incurred. Aircraft violating or about to violate prohibited airspace are often warned beforehand on 121.5 MHz, the emergency frequency for aircraft.