The estate of the letters of Brunner is partly fragmentary, which is mainly due to the persecution of Jews during the Nazi regime: Brunner and many of his correspondents were of Jewish descent and were either killed in extermination camps or were able to save themselves with difficulty.


Many letters exist today only because during the occupation of the Netherlands in the Second World War they were buried behind the grave of Brunner, where they were not victimized by bomb attacks.


After the Second World War there was no chance of a publication. Brunner's correspondence was at first part of the Brunner archive in The Hague, managed by Magdalena Kasch, and was handed over to the Leo Baeck Institute in New York in the seventies.


Other letters can be found in the Swiss Literary Archives in Berne, in the National Library of Israel in Jerusalem, in the archives of Columbia University New York, in the International Institute of Social History in Amsterdam, in the Berlin State Library, in the Federal Archives in Koblenz, and in the archives of the Akademy of Arts, Berlin.


In 2008 the two large Brunner letter collections from the Leo Baeck Institute New York and from the archives of the International Constantin Brunner Institute (ICBI) The Hague were brought together in Berlin. They are now under the roof of the Jewish Museum at the Leo Baeck Institute in Berlin, have been cataloged, micro-filmed and digitized. All documents have now become accessible online. To the online catalog here.


A selection of the letters was published in October 2012 by the publishing house Wallstein in Göttingen. For further information and order data see here.