The article gives a review of inedited sources dealing with the Belgian contribution to European integration in the years 1945-1955. Such sources are kept in the Algemeen Rijksarchief (the Belgian Central Archives), in the Parliament, various ministerial departments, the Navorsings- en Studiecentrum voor de Geschiedenis van de Tweede Wereldoorlog (the Research- and Study Centre for the History of the Second World war), study centres of the major political parties, a number of non-governmental organizations as well as the private archives of a number of politicians.