This book analyzes one of the most relevant issues of investment arbitration, which has extremely important practical consequences. Starting from an analysis of the sources of parallel proceedings and from a study of the reasons for the proliferation of international investment arbitrations arising from the same facts. The author argues that - at the admissibility stage of arbitral proceedings - the application of certain principles (namely abuse of process, res judicata and collateral estoppel) could, if such principles are broadly interpreted, offer practical solutions to the issue. This interpretation finds support in several awards and legal writings and the conclusions reached in the book are highly desirable from the perspective of investment arbitration as a public means of disputes settlement.The book is of interest to scholars and practitioners working on international law and international arbitration.