This report analyzes the establishment of an air defense identification zone (ADIZ) over the East China Sea in November 2013 by the People's Republic of China (PRC, or China), international responses to that action, its consequences, and related matters of national interest and strategy. The report examines the legal, military, and diplomatic aspects of China's ADIZ, with a focus on U.S. interests and issues of concern to Congress. The most salient issues include bilateral relations with the PRC, relations with U.S. partners in East Asia, U.S. military posture in the Asia-Pacific region, and international law (especially regarding freedom of navigation). The 113 th Congress addressed China's ADIZ in resolutions S.Res. 412 and H.Res. 714 , among others. The 114 th Congress may choose, in its oversight of U.S. foreign and defense policy and in its legislative activities, to further shape U.S. responses to China's ADIZ and related policies. The PRC's East China Sea ADIZ has implications for, and is influenced by, numerous other issues. 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] 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. While many nations have established one or more ADIZs in the interest of national security, no international agreement or consensus exists regarding the establishment of or the flight operations and air traffic procedures related to such airspace. ADIZs are located primarily over waters off coastal nations and often include large swaths of airspace beyond the boundaries of territorial lands and waters. In 1948, the U.S. Air Force designated several offshore areas as "active defense areas" or "defense zones." From these, the first ADIZs in the world were established in 1950, under an Executive Order directing the Secretary of Commerce to exercise security control over aircraft. Various defense zones were redesignated as ADIZs. The present-day U.S. ADIZs, including the contiguous U.S. ADIZ (over Atlantic, Pacific, and Gulf of Mexico waters, see Figure 1 ), the Alaska ADIZ, the Guam ADIZ, and the Hawaii ADIZ, are codified in Title 14, Part 99, of the Code of Federal Regulations , along with the procedural requirements for flights operating in these designated areas. They are predominantly located over water and typically do not extend to the shore, leaving a narrow strip of sovereign airspace parallel to the coastline that is not within the ADIZ. U.S. ADIZ procedures apply to aircraft operating to, from, or within the United States through a designated ADIZ. The ADIZ procedures do not apply to U.S. military and law enforcement aircraft. Foreign aircraft, including foreign military aircraft, may generally operate freely within any portion of an American ADIZ not considered part of domestic airspace without complying with the regulatory procedures for communications and positive aircraft identification so long as they do not intend to enter or depart from sovereign U.S. airspace. If however, foreign state or military aircraft are authorized to operate to or from sovereign U.S. airspace, they generally would be required to follow all applicable ADIZ procedures when operating in an ADIZ. Procedural regulations mandate that all civil aircraft entering an ADIZ maintained by the United States must be equipped with an operating two-way radio, and in general, unless otherwise authorized by air traffic control, an operating radar beacon transponder with altitude reporting capability. By regulation, flights operating within an ADIZ must file a flight plan and provide required information regarding aircraft and operator identification and planned flight trajectory. Pilots must make position reports to air traffic controllers before entering the ADIZ and upon reaching certain designated reporting points, and must notify controllers of any deviations from the flight plan or from air traffic clearance instructions. Additionally, regulations require that aircraft operating in an ADIZ comply with any special security instructions that the Federal Aviation Administration (FAA) may issue. The Canadian ADIZ, along with the U.S. ADIZ, is jointly monitored and enforced by the militaries of both nations. Monitoring and enforcement of ADIZ procedures is the responsibility of the North American Aerospace Defense Command (NORAD), a bi-national United States and Canadian organization charged with the missions of aerospace warning and aerospace control for North America. In the United States, FAA handles flight plans and requests, while in Canada NAV CANADA provides air traffic services for aircraft operating within the ADIZ under Canadian civil aviation regulations set forth by Transport Canada. Procedures and regulations are harmonized across both the U.S. and Canadian ADIZ regions. Among Asian countries, Japan, South Korea, Taiwan, the Philippines, Vietnam, Burma, and India all established ADIZs more than 20 years ago. Japan's ADIZ first came into existence during post-World War II reconstruction to aid Japanese civil air defense initiatives, and Japan codified the zone in 1969. South Korea's ADIZ came into existence in 1951, during the Korean War, to aid military forces in positive identification of non-hostile civil aircraft. See Table 1 for a comparison of ADIZ features among the United States and selected Asian countries. Since ADIZs predominantly lie beyond nations' land borders, their treatment in international law and international policy debates has been a complex and contentious issue. International civil aviation matters are generally encompassed in the Convention on International Civil Aviation, commonly known as the Chicago Convention, which the member nations first agreed to in Chicago, IL, in December 1944 and fully ratified in 1947. While the Chicago Convention does not address or refer to ADIZs specifically, its first two articles define national sovereignty and territorial claims with respect to airspace. Specifically, the Chicago Convention maintains that each nation has complete and exclusive sovereignty with respect to airspace above all recognized territories, including all land areas and all adjacent territorial waters under its sovereignty, suzerainty, protection, or mandate. The 1982 United Nations Convention on Law of the Sea (UNCLOS) informs present day international policy discussion regarding territorial waters and, consequently, matters of airspace sovereignty beyond land borders. In general, UNCLOS provides that nations maintain exclusive sovereignty within territorial seas, extending 12 nautical miles (roughly 14 statute miles) offshore. Additionally, UNCLOS defines "contiguous zones" as additional outer bands extending to 24 nautical miles (roughly 27.5 statute miles) from shore, in which a nation may exercise certain controls and enforcement actions to protect itself from infringement of its customs, fiscal, immigration, or sanitary laws and regulations. Further, UNCLOS allows nations to establish exclusive economic zones (EEZs), extending as far as 200 nautical miles (roughly 230 statute miles) offshore, in which a nation can exert control over activities impacting economic resources including fishing, mining, oil exploration, and pollution. UNCLOS maintains that all nations may enjoy the freedoms of navigation and overflight within these zones, as well as other internationally lawful uses, which in general may include military exercises, reconnaissance, and other civilian and military use. The United States has not ratified UNCLOS, unlike China, Japan, and South Korea. Most governments contend that transiting vessels and aircraft maintain high seas freedoms in both contiguous zones and in EEZs, although China and some other nations dispute this interpretation. China, Brazil, and some other coastal nations contend that they have some rights to regulate certain military traffic flying above their EEZs. In contrast, the United States asserts the rights of U.S. military aircraft to transit through ADIZs without complying with procedural regulations established for the ADIZ so long as the aircraft do not intend to enter the nation's sovereign airspace and are not otherwise under the guidance of air traffic control. China's assertion of control of international airspace overlying its EEZ and U.S. disagreement with this assertion played a part in the April 2001 collision of a People's Liberation Army (PLA, the official name of the Chinese military) J-8 fighter with a U.S. Navy EP-3 reconnaissance aircraft over the South China Sea. The mishap resulted in the death of the PLA pilot and the detention and interrogation of the U.S. Navy crew, which was forced to make an emergency landing on the PRC's Hainan Island.