This book evaluates the core of the concept of legitimate expectations from first principles in moral philosophy. It adopts an unconventional approach by examining this topic from a deep, philosophical perspective and delves into the debates on the binding nature of promise in moral philosophy. It then develops a doctrinal structure for the standard of protection. The author places the key premise of the book on the possibility of deriving firm conclusions from the debate and on creating a set of precise and prescriptive 'guidelines of the application of legitimate expectations'. The features of this book are threefold: first, a significant body of literature on moral philosophy is assimilated; second, core philosophical principles are extracted and expressed as a normative framework to resolve concrete cases; third, the author analysed a vast number of investment treaty awards against the underlying framework.

'This book presents a fresh outlook on the theory of legitimate expectations as applied prominently in the jurisprudence of investment tribunals. Building on detailed knowledge of the relevant cases, Teerawat Wongkaew manages to offer fascinating insights into the underlying philosophical theories of legitimate expectations. He makes a compelling argument in favour of a reliance conception that introduces core elements of the traditional estoppel principle into the debate and provides a suitable framework of analysis.'

August Reinisch - University of Vienna

'By drawing on the moral philosophy of promise, this book takes a novel, unexplored route in developing a doctrinal structure and theory for the understanding and application of the concept of legitimate expectations. It is independent and unconventional thinking at its best and shows that legal philosophy and international investment law have more potential for fruitful interaction than many would have thought.'

Stephan Schill - University of Amsterdam

'Teerawat Wongkaew's work is a brilliant effort to provide a moral and carefully nuanced basis for the use of legitimate expectations that both grounds as well as limits the use of this concept as the basis of responsibility of states. The philosophical and moral rationalisation it provides will guide scholarship on the subject even when it provokes dissent. The capacity of this work to provoke thinking on a subject that deeply affects the legitimacy of investment arbitration will set it apart as the most meaningful work to have been written thus far on this subject.'

M. Sornarajah - National University of Singapore

'This is indeed a serious and thoughtful attempt at clarifying a concept too often invoked outside any elaborated definition; a book which, for sure, will be as interesting and useful for practitioners as for scholars interested in the current development of the international law of investments.'

Pierre-Marie Dupuy - Graduate Institute of International and Development Studies, Geneva