The objective of the study is to make a comparison between the standard of national treatment in international investment law and the standard of national treatment in WTO law. Even if similar issues may appear under EU law, the focus of this study is international investment law and WTO law. We will look at international treaties, legal writings and judicial sources (arbitral awards, and panel or Appellate body decisions) in order to establish the similarities and differences are between the two standards of treatment. The study will aim to provide a clear analysis of article 3 paragraphs 1–3 of GATT (General Agreement on Tariffs and Trade) as well as different provisions contained in investment treaties, in reference to the standard of national treatment. The study hopes to offer some guidance on how the two standards of treatment relate to one another, which could prove very helpful for different national and international organizations and institutions when negotiating Investment Treaties or Free Trade Agreements.