Even though widely recognized as one of the core disciplines of international trade law, the interpretation of national treatment obligation has been long marked by legal indeterminacy. More recently, a series of landmark cases, including US – Clove Cigarettes, US – Tuna II (Mexico), US – COOL and EC – Seal Products, have fundamentally changed our collective understanding of the NT obligation in the GATT/WTO system. The purpose of this article is to take stock of what we have already known about the NT obligation in the WTO law (including the GATT 1994 and the TBT Agreement), identify some unresolved issues and discuss the options for the WTO Appellate Body to bring more clarity to the NT obligation in future adjudications.