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.