This monograph offers a detailed and distinctive analysis of corporate nationality under international investment law, covering the ICSID Convention and the investment treaty framework. It takes the reader back to the basics, threading through the concepts of jurisdiction, nationality, and corporate personality to give a clear context to the discussion of corporate nationality under international investment law, at a time when international investment is dominated by multinational business enterprises operating in a globalised economy. The book examines different understandings of corporate personality and nationality under a selection of jurisdictions and public international law. It also offers an in-depth analysis of approaches found in ICSID arbitral awards and in investment treaty practice, distilling the problematic areas and discussing the impacts of the areas of concern. It evaluates the techniques developed to address problems and puts forward suggestions for effective and balanced solutions to the questions of corporate nationality and personal scope of investment protection.