On November 23, 2013, China declared an Air Defence Identification Zone (ADIZ) in the East China Sea. This ADIZ overlaps with the existing ADIZs of Japan, Korea and Taiwan. The Chinese ADIZ raised concerns from various governments and commentators in the region. First, does this ADIZ violate the principle of freedom of overflight in areas beyond territorial sea? Second, can China use the ADIZ to strengthen its claim to sovereignty over disputed islands? Third, does the declaration of an ADIZ strengthen China’s argument that foreign military aircraft have no right to engage in surveillance and reconnaissance activities in the airspace above its exclusive economic zone? Fourth, does China intend to declare an ADIZ in the airspace above the South China Sea, and if so, would this exacerbate existing disputes over sovereignty claims and maritime claims in the South China Sea? This chapter attempts to answer some of these questions. First, the chapter looks at two major principles of international law governing airspace, the principle of national air sovereignty and the principle of freedom of overflight. Second, the chapter examines the status of ADIZ under international law and provides an overview of State practice with regard to ADIZ. Third, it examines China’s ADIZ in the East China Sea and the reactions of other States to China’s East China Sea ADIZ. Fourth, it discusses the implications of a possible Chinese ADIZ in the South China Sea, especially in light of the Arbitral Award issued on 12 July 2016 in the Philippines/China South China Sea disputes. Although it has been alleged that the Chinese ADIZ is contrary to the practice of other States the practice of States that have declared ADIZs is neither uniform nor consistent. The chapter therefore recommends that interested States discuss the development of ‘rules of the road’ for ADIZs based on best international practice in order to minimise the risk of collisions or other incidents.