The debate over regionalism and the multilateral trading system intensifies in the WTO as dozens of regional trade agreements are declared to be exceptions to GATT's most-favoured nation obligation. Commentators debate whether such agreements are stepping stones to freer world trade, and WTO Members remain unsettled on criteria to determine the compatibility of agreements with the multilateral trading system. This work addresses legal aspects of GATT Article XXIV and its internal trade requirements as they define the WTO gateway for regional trade agreements. The case for a narrow avenue is made by exploring historical foundations in the Havana ITO negotiations and later difficulties of applying provisions to developed/developing country free-trade areas. The external economic effects for the trade of non-members will remain of concern, but rules of origin and regional safeguard regimes can also affect intra-regional trade between large and small members. The GATT-47 practice is contrasted with WTO developments as dispute settlement reports have established the conditional legal nature of the regional exception. A treaty law argument is made that GATT/WTO rules retain continuing validity for regional members. Implications for the WTO review process are considered. Regional Trade Agreements in the GATT/WTO is addressed to trade lawyers and academics, international economists, and policy professionals working with non-discrimination issues and the question of legal compatibility of regional agreements in the WTO.