An Air Defense Identification Zone
) is airspace
over land or water in which the identification, location, and control of civil aircraft
is required in the interest of national security
They extend beyond a country's airspace to give the country more time to respond to foreign and possibly hostile aircraft.
The authority to establish an ADIZ is not given by any international treaty nor prohibited by international law and is not regulated by any international body.
The first ADIZ was established by the United States soon after World War II
. Following the incident of September 11, 2001 (September 11 attacks
) when civilian commercial aircraft was abused for mass destruction, ADIZ became prominent as a method to prepare or control a foreign aircraft from entering their territory. About 20 countries and regions now have such zones including Canada
and the United Kingdom
, People's Republic of China
, South Korea
, United States
and more. Russia
and North Korea
have unofficial ADIZ for themselves as well. 
Usually such zones only cover undisputed territory, do not apply to foreign aircraft not intending to enter territorial airspace, and do not overlap.
The United States maintains four zones: The Contiguous US ADIZ; Alaska ADIZ; Guam ADIZ; and Hawaii ADIZ.
Under U.S. law and policy, the zone applies only to commercial aircraft intending to enter U.S. airspace.
An air defense command and control structure was developed in 1950, creating five Air Defense Identification Zones around North America. If radio interrogation failed to identify an aircraft in the ADIZ, the Air Force launched interceptor aircraft to identify the intruder visually. The air defense system reached its peak in 1962, however with the deployment of the SS-6 ICBM
in the USSR, strategic threats shifted overwhelmingly to ICBM attacks, and bomber intrusions were considered to be less of a threat. It does apply to aircraft passing through the zone to other countries.