International airspace, that is, airspace outside national airspace, goes by multiple names. It can be simultaneously part of an air defence identification zone (ADIZ), airspace over an exclusive economic zone (EEZ), a flight information region (FIR), and an aeronautical/maritime search and rescue region (SRR). Each category entails different rights and duties for coastal and user states, many of which are not internationally settled. While acknowledging the general tendency for coastal states to assert claims over maritime areas adjacent to their territory (the concept of “creeping jurisdiction”), Stewart starts this book by pointing out that “a comprehensive, contemporary examination of the impact of assertions of coastal state jurisdiction beyond that which is explicitly granted under international law, on overflight rights, specifically, was elusive” (p. 2). In this well-researched book, she investigates the jurisdiction of coastal states over the operation of foreign aircraft in international airspace adjacent to their coasts.

Stewart hints that three significant events sparked her research; namely, China's opposition to the United States aircraft flying in international airspace in the South China Sea over its artificial islands; the Gulf states’ ban on Qatari-registered aircraft entering international airspace within their FIRs; and China's adoption of an ADIZ with several features that resulted in pushback from other states. Chapter 4 of the book, with its focus on FIR and ADIZ, is a significant contribution since in-depth analyses on those topics are surprisingly rare. One possible criticism is that, instead of having FIR and ADIZ in the same chapter, addressing them in two separate chapters could have clarified the point. As Stewart explains, FIR has its basis in international civil aviation law (namely, the Chicago Convention of 1944),Footnote ¹ while ADIZ has no foundation in international law.

The book's biggest strength is the author's intimate knowledge of air law and the law of the sea. Through an integrated examination of these two specialized fields of international law, she effectively presents the “ambiguity in international law in terms of where the balance sits between the rights of the coastal state and the rights of the users of the airspace in the exercise of their freedom of overflight” (p. 241). To alleviate fragmentation of the law governing the use of international airspace, she calls for closer cooperation between the International Civil Aviation Organization (ICAO) and the International Maritime Organization (IMO), such as by issuing joint guidance on the text of the treaty. ICAO and IMO had already done something similar when they published the International Aeronautical and Maritime Search and Rescue (IAMSAR) Manual. While emphasizing that freedom of overflight is a fundamental principle in international airspace, Stewart firmly concludes that the international community must closely scrutinize the practices of coastal states as to their legitimacy under relevant international law.

This book is particularly helpful in understanding relevant international laws and state practices in international airspace.