Which principle of the World Trade Organization requires equal trade treatment for all WTO members?

The WTO principle requiring equal trade treatment for all members is most-favoured-nation treatment.

Often abbreviated MFN, this principle means that a trade advantage granted by one WTO member to one member should generally be extended immediately and unconditionally to all other WTO members. It is a central non-discrimination rule in the multilateral trading system.

The name can be misleading: MFN treatment does not mean giving one country a uniquely preferred status. In WTO usage, it means treating trading partners equally. The main goods rule appears in Article I of the General Agreement on Tariffs and Trade, while related provisions apply to services and intellectual property.

MFN has recognized exceptions, including certain free-trade agreements, customs unions and preferential arrangements for developing economies. It is different from national treatment, which concerns equal treatment of imported and domestic products after importation.