This is the first systematic analysis of multiple proceedings arising from investor-state disputes, including proceedings before multiple arbitral tribunals, the domestic courts of host states, and other forums such as the European Court of Human Rights. It seeks to identify clear, predictable, and sensible coordination mechanisms and to suggest an application of these mechanisms that reduces jurisdictional fragmentation, jurisdictional competition, and the potential for abuse of the complexities of the system of international investment protection. The author explains how uncertainty in the area extends to several issues: there are doubts as to which forums have jurisdiction over a dispute and to what questions exactly this jurisdiction extends; there are doubts as to the mechanisms that should be applied to coordinate multiple proceedings (including consolidation, hierarchical coordination mechanisms, lis pendens and res judicata, and general principles of comity and prohibition of abuse of process) and how these mechanisms relate to each other; there are also doubts as to the law applicable to coordination mechanisms and the specifics of their application.The book begins with an examination of the characteristics of the international investment framework that frequently lead to multiple proceedings. It then addresses the issue of determining jurisdiction, a prerequisite for the application of any mechanism for further coordination. The author goes on to examine the role of agreed coordination (such as the consolidation of proceedings) versus 'default' coordination mechanisms; the role of hierarchy of forums in coordination, which he argues is relevant when coordinating treaty proceedings on the one hand and non-treaty proceedings on the other; the principles of lis pendens and res judicata, which he argues apply only under limited circumstances; and concludes with the establishment of guidelines regarding the application of the principles of comity and the prohibition of abuse of process. This inherently practical subject is exclusively concerned with the existing law and seeks to provide serviceable solutions to the uncertainty facing practitioners and scholars in the current climate of investment law.