A partial list of CRS reports on related topics includes:
CRS Report R42930, Maritime Territorial Disputes in East Asia: Issues for Congress , by [author name scrubbed], [author name scrubbed], and [author name scrubbed]
CRS Report R42784, Maritime Territorial and Exclusive Economic Zone (EEZ) Disputes Involving China: Issues for Congress , by [author name scrubbed]
CRS Report R42761, Senkaku (Diaoyu/Diaoyutai) Islands Dispute: U.S. Treaty Obligations , by [author name scrubbed]
CRS Report R41108, U.S.-China Relations: An Overview of Policy Issues , by [author name scrubbed]
CRS Report RL32496, U.S.-China Military Contacts: Issues for Congress , by [author name scrubbed]
CRS Report R41952, U.S.-Taiwan Relationship: Overview of Policy Issues , by [author name scrubbed] and [author name scrubbed]
CRS Report RL33436, Japan-U.S. Relations: Issues for Congress , coordinated by [author name scrubbed]
CRS Report R41481, U.S.-South Korea Relations , coordinated by [author name scrubbed]

	Background and History of ADIZs

An ADIZ is a designated area of airspace over land or water within which a country requires the immediate and positive identification, location, and air traffic control of aircraft in the interest of the country's national security. ADIZs are located primarily over waters off coastal nations and often include large swaths of airspace beyond the boundaries of territorial lands and waters. Additionally, regulations require that aircraft operating in an ADIZ comply with any special security instructions that the Federal Aviation Administration (FAA) may issue. The ECS ADIZ asserted coverage of the airspace over the Senkaku Islands, which are administered by Japan and claimed by the PRC as the Diaoyu Islands and by Taiwan as the Diaoyutai Islands. Moreover, the ECS ADIZ overlaps with the existing ADIZs of Japan, ROK, and Taiwan. The rules warn that "China's armed forces will adopt defensive emergency measures to respond to aircraft that do not cooperate in the identification or refuse to follow the instructions." Chinese officials and scholars defended China's right to establish an ADIZ, but officials from the United States, Japan, South Korea, and other countries strongly protested the move (see later sections). There are several possible explanations for the PRC's apparent restraint in enforcing its ADIZ regulations. Relatedly, Beijing might have set up the ECS ADIZ for prestige. Responses

Promptly after the PRC announced the ECS ADIZ on November 23, 2013, Defense Secretary Hagel called the development a destabilizing attempt to alter the status quo, stated that the announcement would not change U.S. military operations, and reaffirmed that the U.S.-Japan Mutual Defense Treaty applies to the Senkaku Islands. Reportedly, the United States and Japan agreed to increase their reconnaissance and surveillance activities in the East China Sea, presumably to monitor Chinese practices in the new ADIZ. Guidance to Commercial Airlines "). Furthermore, the new overlapping area could increase the risk of an incident. Implications for U.S. Policy

The PRC's ECS ADIZ has implications for U.S. policy in terms of the potential for conflict, escalation of tension, Sino-Japanese tensions, a strategic challenge to the United States, and U.S.-China military-to-military exchanges. The action is consistent with an assessment in 2013 by several experts that found that the most likely challenge to the U.S.-Japan alliance over the next 15 to 20 years is not a full-scale military conflict between China and Japan or the United States but the more likely attempts by China to use coercively its growing military capabilities to influence or resolve disputes with Japan in China's favor without resorting to an attack. He urged the Administration to consider China's actions as the use of coercion to change the status quo. 412 states that the Senate "urges the Government of the [PRC] to refrain from implementing the [ECS ADIZ], which is contrary to freedom of overflight in international airspace ... " The resolution reaffirms the strong support of the U.S. Government for freedom of navigation and other internationally lawful uses of sea and airspace in the Asia-Pacific region and states that it is U.S. policy, inter alia, to assure the continuity of U.S. operations in that region. The United States neither recognizes nor accepts China's declared East China Sea ADIZ and has no intention of changing how we conduct operations in the region. Text of ECS ADIZ Announcement

The PRC MND issue the following statement on November 23, 2013:
The Ministry of National Defense of the People's Republic of China, in accordance with the Statement by the Government of the People's Republic of China on Establishing the East China Sea Air Defense Identification Zone, now announces the Aircraft Identification Rules for the East China Sea Air Defense Identification Zone as follows:
First, aircraft flying in the East China Sea Air Defense Identification Zone must abide by these rules.
In November 2013, the People's Republic of China (PRC, or China) announced that it would establish an "East China Sea Air Defense Identification Zone (ADIZ)," covering a large swath of airspace over the East China Sea, including over small islands that are the subject of a territorial dispute among Japan, the PRC, and Taiwan. Beijing did not formally consult with other countries prior to the announcement, and its initial statement seemed to warn that China might use force against aircraft that did not follow its ADIZ guidelines. Senior officials from the United States and East Asian countries criticized China's action and raised concerns that the new ADIZ could escalate tensions surrounding the territorial dispute and even lead to conflict.
Some key considerations for Congress are the potential for military conflict in the East China Sea, escalation of tensions over the territorial dispute, challenges to the U.S.-Japan alliance, and the impact on U.S.-China relations, including military-to-military exchanges.
An ADIZ is an area of airspace beyond a country's sovereign territory within which the country requires the identification, location, and air traffic control of aircraft in the interest of its national security. There is no international law that specifically governs ADIZs, although various norms pertain, especially freedom of navigation. The Convention on Civil Aviation advises that all nations refrain from the use of weapons against civilian aircraft. The United States was the first country to establish an ADIZ, which it did in 1950 during the Cold War with the Soviet Union.
There are several possible reasons why the PRC designated its "East China Sea ADIZ" (ECS ADIZ). The ADIZ appears to be part of an effort by China to challenge Japan's administration of the disputed islands, known as Senkaku in Japan, Diaoyu in China, and Diaoyutai in Taiwan. The ECS ADIZ may also be intended as a means to bolster both China's own claims to the islands and its justification for opposing U.S. military surveillance activities near its airspace. In the initial period after the PRC announcement, the PLA did not take "defensive emergency measures" against aircraft that ignored the Chinese ADIZ directives.
In addition to criticisms by the U.S. Secretaries of State and Defense that the ECS ADIZ was "destabilizing" and increased the risks of conflict in the region, the United States announced that it "neither recognizes nor accepts China's declared East China Sea ADIZ." As of early 2015, the U.S. military continues to fly aircraft through the zone without notifying China or responding to requests for identification. The Federal Aviation Administration (FAA), however, distributed China's requirements for operating in the ECS ADIZ to commercial airlines as part of its routine dissemination of Notices to Airmen (NOTAMs).
Japan, South Korea, and Taiwan each voiced opposition to China's designation of the ECS ADIZ, which overlapped with their pre-existing ADIZs, and have continued normal military practices in the zone. South Korea requested that China redraw the boundary to remove this overlap, but Beijing refused the request, prompting Seoul to extend the boundaries of its ADIZ in December 2013. Japan called the PRC's action an attempt to change the status quo on the Senkaku Islands by coercion. The U.S.-Japan Mutual Defense Treaty applies to the Senkaku Islands because they are administered by Japan.
This report analyzes the legal, diplomatic, and security implications of the ECS ADIZ for U.S. interests. The concluding section briefly discusses some policy options for Congress and for U.S. policy in general.