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.