Three pillars of the European Union in the context of "European Economic Community"

The European Economic Community (EEC) was a regional organisation created by the Treaty of Rome of 1957, aiming to foster economic integration among its member states. It was subsequently renamed the European Community (EC) upon becoming integrated into the first pillar of the newly formed European Union (EU) in 1993. In the popular language, the singular European Community was sometimes inaccurately used in the wider sense of the plural European Communities, in spite of the latter designation covering all the three constituent entities of the first pillar. The EEC was also known as the European Common Market (ECM) in the English-speaking countries, and sometimes referred to as the European Community even before it was officially renamed as such in 1993. In 2009, the EC formally ceased to exist and its institutions were directly absorbed by the EU. This made the Union the formal successor institution of the Community.

The Community's initial aim was to bring about economic integration, including a common market and customs union, among its six founding members: Belgium, France, Italy, Luxembourg, the Netherlands and West Germany. It gained a common set of institutions along with the European Coal and Steel Community (ECSC) and the European Atomic Energy Community (EURATOM) as one of the European Communities under the 1965 Merger Treaty (Treaty of Brussels). In 1993, a complete single market was achieved, known as the internal market, which allowed for the free movement of goods, capital, services, and people within the EEC. In 1994 the internal market was formalised by the EEA agreement. This agreement also extended the internal market to include most of the member states of the European Free Trade Association, forming the European Economic Area, which encompasses 15 countries.

The European Communities (EC) were three international organizations that were governed by the same set of institutions. These were the European Coal and Steel Community (ECSC), the European Atomic Energy Community (EAEC or Euratom), and the European Economic Community (EEC), the last of which was renamed the European Community (EC) in 1993 by the Maastricht Treaty establishing the European Union. The European Union was established at that time more as a concept rather than an entity, while the Communities remained the actual subjects of international law impersonating the rather abstract Union, becoming at the same time its first pillar. In popular language, however, the singular European Community was sometimes used interchangeably with the plural phrase, in the sense of referring to all three entities.

The European Coal and Steel Community ceased to exist in 2002 when its founding treaty expired. The European Community was merged with the second and third EU pillars by the Treaty of Lisbon in 2009, finally allowing the European Union to move beyond being only a concept and to assume the shape of a legally incorporated international organization with juridical personality, designated as the legal successor to the Community. However, the reformed EU has not become entirely unified, because Euratom, though governed with the EU by the common set of institutions, has been retained as an entity distinct from the EU, along with a number of other international entities, such as the European Investment Bank, the European University Institute, the European Stability Mechanism, and the Unified Patent Court.

The European Political Co-operation (EPC) was the common term for the co-ordination of foreign policy between member states of the European Communities (EC) from its inception in 1970 until the EPC was superseded by the new European Union's (EU) Common Foreign and Security Policy (CFSP) pillar upon the entry into force of the Maastricht Treaty in November 1993.