FACTBOX: What is NATO?

(Reuters) - A three-day summit, the largest in NATO's history, starts on Wednesday.

The summit could mould the West's relations with Russia for years to come and show whether the U.S.-led alliance has the resolve to win the war in Afghanistan.

Here are some facts about NATO:-

* WHAT IS NATO?:

-- The North Atlantic Treaty Organization was created in 1949 as a bulwark against the Soviet Union. The 26-nation regional defense alliance is committed to enhancing the stability, well-being and freedom of its members by means of a system of collective security enshrined in Article 9 of the North Atlantic Treaty. The alliance's HQ is in Brussels.

* NATO MEMBERS:

-- Belgium, Bulgaria, Canada, Czech Republic, Denmark, Estonia, France, Germany, Greece, Hungary, Iceland, Italy, Latvia, Lithuania, Luxembourg, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Turkey, United Kingdom, United States.

* MAJOR MISSIONS:

-- NATO helped end conflicts in Bosnia, Kosovo and head off a civil war in the former Yugoslav Republic of Macedonia. Its forces are now helping to bring stability to Kosovo and Afghanistan -- its biggest ground combat operation.