On 6 April 1957, Walter Hallstein, State Secretary at the Foreign Office of the Federal Republic of Germany (FRG), delivers an address at the University of Stuttgart in which he gives an account of the successive stages of European integration, emphasising certain aspects of the Treaties establishing the European Economic Community (EEC) and the European Atomic Energy Community (EAEC or Euratom), signed 12 days earlier in Rome.

On 29 September 1967, the Commission, not being in possession of all the information that is required if it is to deliver the Opinion provided for by the Treaties, delivers a preliminary Opinion on the applications for accession to the European Communities submitted by the United Kingdom, Ireland, Denmark and Norway.

On 19 January 1972, the European Commission delivers a favourable opinion in response to applications from the Kingdom of Denmark, Ireland, the Kingdom of Norway and the United Kingdom of Great Britain and Northern Ireland for membership of the European Communities.