The EEC was established in the Treaty of Rome, after objections of impeached sovereignty from members of the ECSC. The French President, de Gaulle, wanted an intergovernmental political co-operation, a shift away from the supranational character of the ECSC.  The idea of creating a European defence community was rejected by many; in the EEC therefore defence was left up to organisations such as NATO and the Western European Union.

The aim of the EEC was to create a common market, whereby there would be a removal of all barriers to trade within the union and a fixed custom tariff to promote trade. It built upon the idea behind the ECSC: that economic co-operation would lead to a peaceful Europe. The two new institutions of the EEC were the Council and the Commission. The Commission's role was to ensure the implementation of policy, represent the EEC in international negotiations and to propose new policy.

Neo-functional theory explains the establishment of the EEC with the process known as spill-over. This theory was pioneered by Ernst Haas, who explained spill-over as the integration of wider interest (political, economic) to form a common market. This explained the initial success of the EEC but failed to explain the 1960s. Another theory, known as liberal intergovernmentalism, was developed by Andrew Marsalis.  This theory stated that the national interest - and specifically, national governments - controlled the EU policy setting agenda.

The EEC was to become known as the EC in the Treaty of Maastricht. This went on to form the basis of the first pillar of the European Union. Its responsibilities included the continual running of the internal market as well as the environmental, social and economic policy. This would also include the monetary union and policy dealing with immigration. This pillar would be supranational in nature.