Its decisions are absolute and every member must abide by its rulings.

So, when the US and the European Union are in dispute over bananas or beef, it is the WTO which acts as judge and jury.

Four principles

The WTO has 134 members and makes decisions on a basis of unanimity.

No country can wield a power of veto.

The principles which members sign up to are: extending trade concessions equally to all WTO members, aiming for a freer global trade with lower tariffs everywhere, making trade more predictable through the use of rules and bringing about more competition by cutting subsidies.

The details of how much countries are prepared to cut tariffs and trade barriers are hammered out at large sessions of talks, so-called trade rounds, of which there have been eight since 1947.

The next session is to take place in November, in Seattle.

Given the large number of members these are never straight forward affairs with considerable brinkmanship involved.

One of the more high profile issues recently, alongside the trade disputes between the US and the EU, has been the lobbying by China to become a member.

The WTO is the successor to the General Agreement on Tariffs and Trade, Gatt, which lasted from the end of the second World War to 1995.

WTO decisions can only be reversed by an unanimous vote, just as they can only be made that way.