On 25 September 1956, having been invited to speak at the Grandes Conférences Catholiques in Brussels, the German Chancellor, Konrad Adenauer, delivers an address in which he offers his vision of the role of Europe in the world and expresses some reservations with regard to the establishment of new supranational institutions in Europe.

On 2 February 1957, the delegation of the Bureaux of the three European Assemblies sends a memorandum to the Intergovernmental Conference on the Common Market and Euratom in which the three Assemblies rule out all proposals for the establishment of a fourth European Assembly.

On 14 February 1957, Christian Calmes, Secretary General of the Intergovernmental Conference on the Common Market and Euratom, travels to Bonn to meet Heinrich von Brentano, German Foreign Minister. The discussion focuses on, in particular, the seat of and the allocation of posts in the future institutions of the European Economic Community (EEC) and of the European Atomic Energy Community (EAEC or Euratom). Ultimately, Calmes forwards a memorandum to von Brentano in which he argues in favour of the establishment of a single Council of Ministers for the three Communities.

On 28 February 1957, the Committee of the Heads of Delegation to the Intergovernmental Conference on the Common Market and Euratom proposes that a convention be drawn up which would lay down the required measures and, where appropriate, amend the Treaty establishing the European Coal and Steel Community (ECSC) with a view to the operation of institutions common to several Communities.

On 11 February 1957, in order to limit the number of Community institutions, the Intergovernmental Conference on the Common Market and Euratom draws up a draft convention which provides for the establishment of certain institutions common to the European Coal and Steel Community (ECSC), the European Economic Community (EEC) and the European Atomic Energy Community (EAEC or Euratom).

On 20 March 1957, René Mayer, President of the High Authority of the European Coal and Steel Community (ECSC), forwards to Paul-Henri Spaak, Belgian Foreign Minister and President of the Intergovernmental Conference on the Common Market and Euratom, a letter in which he informs him of the position taken by the High Authority on the powers and responsibilities of the new institutions provided for by the Treaties establishing the European Economic Community (EEC) and the European Atomic Energy Community (EAEC or Euratom).