This book outlines the principles behind the international law of foreign investment, focussing on the law governed by bilateral and multilateral investment treaties. The book traces the purpose, context, and evolution of the clauses and provisions characteristic of contemporary investment treaties, and analyses the case law, interpreting the issues raised by standard clauses. Particular consideration is given to broad treaty rules whose understanding in practice has mainly been shaped by their interpretation and application by international tribunals. In addition, the book describes the dispute settlement mechanisms for enforcing investment law, outlining the operation of Investor v State arbitration. This third edition has been fully updated to reflect the evolution of treaty practice, jurisprudence, and doctrinal opinion, covering new treaties such as the Comprehensive and Progressive Agreement for Trans-Pacific Partnership (CPTPP), United States–Mexico–Canada Agreement (USMCA), and the Comprehensive Economic and Trade Agreement (CETA). Each chapter is introduced by a bibliography of recent publications. Combining a systematic analytical study of the texts and principles underlying investment law with a jurisprudential analysis of the case law arising in international tribunals, the book offers an ideal introduction to the principles of international investment law and arbitration, for students and practitioners alike.