This new edition of what has rapidly become the pre-eminent work on the role of municipal law in investment treaty arbitration is justified not only by the accelerating appearance of investment treaty awards but also by the continuing, serious flaws in the application of international law by investment treaty arbitral tribunals. As a matter of international law, arbitrators need to be attentive to the circumstances where municipal law supplies the necessary substantive legal rule. They will find this book to be the best guide to this complex challenge. The author has maintained the overall structure of the first edition and added a new chapter on Article 42 of the ICSID Convention. Certain descriptions and arguments have been rethought and revised to clarify their significance and their applicability. The treatment focuses on the role of municipal law in providing the substance for concepts such as contracts, property rights, and shareholders’ rights, which are relevant in the international investment treaty context but are not regulated under international law. Among the complex questions considered are the following: - If the application of international law requires a renvoi to municipal law, how should that renvoi be conducted? - In investment disputes, what role, if any, should municipal law have in assessing State attribution under international law? - Should shareholders receive compensation for damages suffered by their company due to a violation of an international obligation vis-à-vis the company? - Does a contractual right exist to foreign investment ‘property’? - Under what conditions may a violation of municipal law become internationally wrongful? - May foreign investors rely on ‘expectations’ as an autonomous source of rights in investment treaty disputes? - Does an alleged breach of an umbrella clause transform a breach of contract claim covered by municipal law into an international law claim? The chapters answer these and many other questions in extraordinary depth, drawing on detailed analyses of the issues and implications posed by major relevant cases and arbitral decisions. The author’s analysis of the unavoidable interaction of municipal law and international law in investment treaty arbitration – and the consequences stemming from rejecting the application of municipal law when relevant – will continue to prove of immeasurable value to arbitrators, arbitration counsel, corporate counsel, and scholars of international law.