General Agreement on Tariffs and Trade (usually abbreviated GATT) functions as the foundation of the WTO trading system, and remains in force, although the 1995 Agreement contains an updated version of it to replace the original 1947 one.

The GATT, as an international agreement, is very similar to a treaty. Under United States law it is classed as a congressional-executive agreement. It is based on the "unconditional most favored nation principle." This means that the conditions applied to the most favored trading nation (i.e. the one with the least restrictions) apply to all trading nations.