Three days ago China’s Ministry of National Defense established an Air Defense Identification Zone (“ADIZ”) for the East China Sea. According to the announcement, foreign aircraft operating within the ADIZ will be subject to a couple of requirements: First, they must provide Chinese authorities with various means of identification, including by reporting flight plans, maintaining two-way radio communications and responding in a timely manner to inquiries, displaying clear marks of nationality, and maintaining the operation of any secondary radar transponders. Second, the aircraft must “follow the instructions” of Chinese authorities. If any aircraft fails to provide identification or follow instructions, “China’s armed forces will adopt defensive emergency measures.” The ADIZ is outlined in red in the map above and, most notably, includes the air territory above the contested Senkaku / Diaoyu Islands. Japan has warned that the ADIZ creates a risk of “unpredictable events,” while Secretary of State John Kerry and Secretary of Defense Chuck Hagel said that they are “deeply concerned” about China’s announcement and committed to defending Japan. The obvious purpose of the ADIZ is to further whittle away at Japan’s de facto control over the Islands. In this post, I want to raise two brief points on the legality of this measure.