- The European Union (EU) consists of 27 member states. Each member state is party to the founding treaties of the union and thereby shares in the privileges and obligations of membership. Unlike members of other international organisations, the member states of the EU have agreed by treaty to shared sovereignty through the institutions of the European Union in some (but by no means all) aspects of government. Member states must agree unanimously for the EU to adopt some policies; for others, collective decision making is by qualified majority voting. Subsidiarity, meaning that decisions are taking collectively if and only if they cannot realistically be taken individually, is a founding principle of the EU. In the 1950s, six core states founded the EU's predecessor European Communities (Belgium, France, Italy, Luxembourg, the Netherlands, and West Germany). The remaining states have acceded in subsequent enlargements. To accede, a state must fulfill the economic and political requirements known as the Copenhagen criteria, which require a candidate to have a democratic, free-market government together with the corresponding freedoms and institutions, and respect for the rule of law. Enlargement of the Union is also contingent upon the consent of all existing members and the candidate's adoption of the existing body of EU law, known as the acquis communautaire. Until 2020, no member state had ever withdrawn or been suspended from the EU, though some dependent territories or semi-autonomous areas had previously left. The UK government invoked Article 50 of the Treaty on European Union on 29 March 2017 to formally initiate the Brexit process. Completion occurred on 31 January 2020 (at 23:00 London time), with all other arrangements remaining in place during a transition period while a free trade agreement is negotiated. (en)
- # In accordance with Article 5, competences not conferred upon the Union in the Treaties remain with the member states.
# The Union shall respect the equality of member states before the Treaties as well as their national identities, inherent in their fundamental structures, political and constitutional, inclusive of regional and local self-government. It shall respect their essential State functions, including ensuring the territorial integrity of the State, maintaining law and order and safeguarding national security. In particular, national security remains the sole responsibility of each member state.
# Pursuant to the principle of sincere cooperation, the Union and the member states shall, in full mutual respect, assist each other in carrying out tasks which flow from the Treaties. The member states shall take any appropriate measure, general or particular, to ensure fulfilment of the obligations arising out of the Treaties or resulting from the acts of the institutions of the Union. The member states shall facilitate the achievement of the Union's tasks and refrain from any measure which could jeopardise the attainment of the Union's objectives. (en)