Written by a leading legal researcher, this book offers a comprehensive study of the principle, a frequently invoked but rarely analysed aspect of investment arbitration. Good Faith in International Investment Arbitration is a thorough and expansive study that considers the application of good faith by arbitral tribunals and parties in international investment disputes, encompassing both procedural and substantive aspects of good faith. Expertly negotiating a complex principle, this book diligently follows the arbitral process from jurisdiction through merits and to cost decisions, identifying the various applications of good faith in investment disputes. The author offers detailed analyses of the role of good faith in defining nationality and investor as well as in pre-dispute admissibility requirements. The study then delves into the ways the principle guides parties' arguments and informs tribunals' decisions regarding evidence, substantive protections, and costs. It further addresses the role of good faith in the behaviour of arbitrators and other actors. This is an essential guide for anyone wishing to understand this important principle that has accompanied the developing system of international investment law.