Dans ses Mémoires, Paul-Henri Spaak, ancien ministre belge des Affaires étrangères, pointe les origines politiques et institutionnelles de la crise de la chaise vide de 1965 et décrit le déroulement des négociations diplomatiques ayant permis, le 29 janvier 1966 à Luxembourg, d'atteindre un compromis politique pour mettre fin à la crise communautaire.

Le 19 janvier 1945, Jules Guillaume, ambassadeur de Belgique à Paris transmet une lettre à Paul-Henri Spaak, ministre belge des Affaires étrangères, dans laquelle il évoque la position de la France quant à la création d'une union douanière entre la Belgique, la France, le Luxembourg et les Pays-Bas.

On 20 October 1948, Raoul de Fraiteur, Belgian Defence Minister, sends a confidential letter to Paul-Henri Spaak, Belgian Prime Minister and Foreign Minister, in which he reviews the decisions adopted by the conference of defence ministers of the five Member States of Western Union.

In this note, Paul-Henri Spaak, Belgian Foreign Minister, informs Émile de Cartier de Marchienne, Belgian Ambassador to London, of the principles and the conditions relating to Belgium’s participation in the Allied military occupation of Germany.

In this letter, Belgian Foreign Minister Paul-Henri Spaak assures the US Government of Belgium's formal support for the United Nations Relief and Rehabilitation Administration (UNRRA) project, but suggests some adaptations given the country's situation.

In this letter sent to the Belgian Foreign Minister, Paul-Henri Spaak, on 3 December 1954, Robert Silvercruys, the Belgian Ambassador to the United States, considers the mindset of US officials following the failure of the European Defence Community (EDC) project.

In this note sent to the Belgian Foreign Minister, Paul-Henri Spaak, on 30 October 1954, Robert Silvercruys, Belgian Ambassador to the United States, tells of the satisfaction in the United States that greeted the signing, on 23 October 1954, of the Paris Agreements establishing Western European Union (WEU).

On 4 April 1955, following the failure of the European Defence Community (EDC), Johan Willem Beyen, Netherlands Foreign Minister, forwards to his Belgian and Luxembourgish counterparts, Paul-Henri Spaak and Joseph Bech, a memorandum in which he proposes the revival of European integration through general, rather than sectoral, economic integration as part of a common market.

On 3 October 1955, Jacques Doublet, Director-General of Social Security in France and Chairman of the Subcommittee for Social Issues in the Intergovernmental Committee established by the Messina Conference, forwards to Paul-Henri Spaak, Belgian Foreign Minister and President of the Committee, a letter in which he gives an account of his meeting in Brussels with the representatives of the International Confederation of Christian Trade Unions (ICCTU) and emphasises their concerns regarding economic and social integration in Europe.

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).