Which WTO principle requires members to extend their best trade treatment to all other WTO members?

The WTO most-favoured-nation principle requires members to extend their best trade treatment to all other WTO members.

Under this principle, if a WTO member lowers a tariff or grants a trade advantage to one trading partner, it generally must provide the same treatment to all other WTO members. The rule is designed to prevent arbitrary discrimination among trading partners and is a central part of the General Agreement on Tariffs and Trade.

The name can be misleading: “most favoured” does not mean that one country receives uniquely privileged treatment. It means equal treatment among covered trading partners. Important exceptions exist for free-trade agreements, customs unions, and certain preferences for developing countries.

The principle is different from national treatment. National treatment concerns equal treatment for imported products after they enter a market, whereas most-favoured-nation treatment concerns discrimination between foreign trading partners.