This book questions whether investment law influences the wider field of general international law, and more specifically, whether approaches adopted by tribunals in investment arbitrations have radiated, or should radiate, into other fields of international law.To answer this question, the book engages in a detailed analysis of pronouncements by investment tribunals on state responsibility, the law of treaties, and general principles of dispute resolution, and evaluates their impact beyond the narrow field of investment law. The perspectives provided in the book highlight how rules of general international law are concretised, specified, and at times moulded in investment arbitration practice. By doing so, the book enhances our understanding of the relationship between general international law and one its most dynamic sub-disciplines.Combining conceptual and practical perspectives, and offering a detailed analysis of the pertinent case law, the book is a plea for a fuller engagement directed at both general international lawyers and international investment lawyers. It will help investment lawyers better understand the role of general international law in their field of practice. General international lawyers will benefit from paying close attention to how investment lawyers apply and interpret rules of general international law.