Book excerpt: Central to this book is an analysis of the obligation upon states to ensure non-discrimination in the form of adherence to the principles of national treatment and most-favoured nation treatment. These are critical principles for both international trade law and international investment law, yet the case-law in both fields reveals significant inconsistencies regarding key elements of non-discrimination. Tribunals have invoked 'regulatory purpose' to assist in identifying relevant discrimination, but have done so without offering a definition of regulatory purpose and in significantly differing ways. This book explains these inconsistencies and offers a new definition of regulatory purpose.