Set up in 1948 by the Treaty of Brussels, the WEU is a European organisation for the purposes of cooperation on defence and security. It consists of 28 countries with four different statuses: Member States, Associate Members, Observers and Associate Partners. All EU countries are full Member States except Denmark, Ireland Austria, Finland and Sweden, which have observer status. The six Associate Members are the Czech Republic, Hungary, Iceland, Norway, Poland and Turkey, and there are seven Associate Partners: Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia and Slovenia.
The Treaty of Amsterdam made the WEU an "integral part of the development of the Union" by giving it an operational capability in the field of defence. The WEU played a major role in the first Petersberg tasks, such as the police detachment in Mostar or cooperation with the police in Albania. However, it now seems to have abandoned that role in favour of developing the Union's own structures and capabilities in the sphere of the common foreign and security policy (CFSP). The transfer of the WEU's operational capabilities to the Union attest to this. The WEU's subsidiary bodies, the Security Studies Institute and the Satellite Centre, were hived off to the Union on 1 January 2002. The Treaty of Nice also deleted from the Treaty on European Union a number of provisions concerning relations between the WEU and the Union. The WEU's main remaining area of responsibility is Article V - collective defence. The transfer of that responsibility to the Union seems to have been deferred.
See:
Collective defence
Common foreign and security policy (CFSP)
European security and defence identity
European Security and Defence Policy (ESDP)
NATO (North Atlantic Treaty Organisation)
'New look' NATO
Petersberg tasks