This collection is published on the occasion of the 250th anniversary of Walter de Gruyter Publishers. The de Gruyter archives of letters, a collection of valuable correspondence with authors, was arranged and enlarged by Otto Neuendorff, who died in 1989. Anne-Katrin Ziesak revised the work and Maria Berger compiled the index. The documents and their contents are described, together with biographical information on each author. The work is in alphabetical order, according to the names of the letter writers. Institutions were treated according to the rules of alphabetic cataloguing. Additional biographical information on the authors - as far as they could be identified - is given. In cases where the dating was unclear, the assumed dates are in brackets, followed by the number and dates of documents as well as their contents. Information about the dates and the recipients is also provided, followed by a short description of the contents. In conclusion, the signature and source of each documents is given. The index includes a list of the persons and the institutions involved and the works, all this material being cross-referenced.