This new book is well-researched, highly informative and, in addition to carefully explaining the regulatory provisions of the General Agreement on Trade in Services (GATS), dares to express firm opinions on the controversial regulatory issues currently under negotiation in the WTO's Working Party on Domestic Regulation (WPDR). On the critical issue of necessity tests, for example, Delimatsis stakes out a workable middle ground, between the idealism often expressed by academics and the frequently sceptical or even negative views held by many trade negotiators. As stated in the introduction, the objective of the study is ‘to come to grips with regulatory diversity in services trade’, noting that, due to the wide-ranging sectoral diversity of services, as well as the differences in preferences, legal culture, domestic priorities, etc. between countries, ‘a given regulatory intervention can be not only sector-specific, but also country-specific’. Reflecting the book's title, Delimatsis argues ‘necessity and transparency are the two crucial tools that allow walking the tightrope between Members’ right to regulate and further services trade liberalization, because, by using them, the fine line between GATS-consistent regulatory intervention and protectionism can be drawn’ (p. 1). The book's writing style is sometimes excessively wordy, needing a bit of editing, but is nonetheless not difficult to follow and definitely worth the effort. The book will undoubtedly become a standard reference for both students and practitioners wishing to have a solid understanding of the complex issues involved. This well-organized book is structured into five main chapters: I. The Multilateral Legal Framework Governing Trade in Services; II. Barriers to Trade in Services; III. Domestic Regulations and the GATS; IV. Creating a Horizontal Necessity Test for Services; and V. Transparency and Domestic Regulations in Services, together with Concluding Remarks. A detailed list of contents, together with the index, make it easy to find specific topics.