stylistic:style_transfer, quality:correction
Member states

Through successive enlargements, the EU and its predecessors have grown from the six founding states of the EEC to 27 members. Countries accede to the union by becoming a party to the founding treaties, thereby subjecting themselves to the privileges and obligations of EU membership. This entails a partial delegation of sovereignty to the institutions in return for representation within those institutions, a practice often referred to as "pooling of sovereignty". In some policies, there are several member states that ally with strategic partners within the union. Examples of such alliances include the Baltic Assembly, the Benelux Union, the Bucharest Nine, the Craiova Group, the EU Med Group, the Lublin Triangle, the New Hanseatic League, the Three Seas Initiative, the Visegrád Group, and the Weimar Triangle.

To become a member, a country must meet the Copenhagen criteria, defined at the 1993 meeting of the European Council in Copenhagen. These require a stable democracy that respects human rights and the rule of law; a functioning market economy; and the acceptance of the obligations of membership, including EU law. Evaluation of a country's fulfilment of the criteria is the responsibility of the European Council.

The four countries forming the European Free Trade Association (EFTA) are not EU members, but have partly committed to the EU's economy and regulations: Iceland, Liechtenstein and Norway, which are a part of the single market through the European Economic Area, and Switzerland, which has similar ties through bilateral treaties. The relationships of the European microstates Andorra, Monaco, San Marino, and Vatican City include the use of the euro and other areas of co-operation.