[Freud's letters as a historical source].

This article introduces the project of a "concordance of letters to and by Freud". It should make the broadly scattered Freud-correspondence more accessible to the historian. (Since the death of Freud, almost 3200 letters written by him and nearly 1200 letters to him have been published.) At the same time principles of methodology are discussed which have to be observed in using letters as historical source material.