Not to be confused with the European Union, the Western European Union (WEU) is a largely dormant European defence and security organization composed of those states members of both NATO and the EU. The WEU was established under the Modified Brussels Treaty, in response to the failure of the European Defence Community treaty. Most of its functions are in the process of being merged into the European Union. The Parliamentary Assembly of the WEU is composed of the delegations of the member states to the Parliamentary Assembly of the Council of Europe, which, fearful for its future existence with the winding up of the WEU, has been lobbying for itself to be recognized as the "European Security and Defence Assembly".

The Secretary-General of the WEU is Javier Solana, who is also Secretary-General of the Council of the European Union and High Representative for the Common Foreign and Security Policy of the European Union. His being head of both organizations permits him to oversee the ongoing transfer of functions from the WEU to the EU.