Who is protected under international investment agreements? Issues relating to nationality of corporate investors have been at the forefront of the recent debates about the present and future of international investment law. Among other things, the ability of firms to deploy their corporate form to cherry pick protections have caused much concern not only among scholars but also policymakers in both developed and developing states. Yet although such debates have generated a considerable body of literature, this book is the first of its kind to explore corporate nationality under international investment law in a critical and comprehensive manner. The book makes a novel contribution to international legal scholarship by tackling the subject with analytical rigour and eloquence in equal measure. In unveiling the systemic issues behind the backlash against international investment law, Yilmaz-Vastardis combines a meticulous analysis of the complex legal issues with a refreshing critical exposition of the context in which the law operates. The book will become a classic and a main point of reference for both scholars of international investment law and experts involved in drafting and interpreting investment treaty instruments.