Part I of this book provides the foundations for the analysis of non-discrimination in general and the concept of ‘likeness’ in particular. As this study focuses on non-discrimination in the context of international trade in services, chapters 1 and 2 set the stage by introducing the principle of non-discrimination in international trade law as well as the particularities of international trade in services and GATS as the main regulatory framework. The subsequent chapter 3 breaks the non-discrimination principle down into its legal elements of ‘less favourable treatment’, ‘likeness’ and ‘regulatory purpose’, analyzing their individual significance and their respective interdependencies. Part I closes with the summary and conclusions under chapter 4, highlighting in particular how the interpretation of each legal element affects the reach and substance of a non-discrimination obligation.