He did extensive ethnological and anthropological work in the Southwest Province, an English-speaking part of Cameroon, and published some 1,000 pages about it. His best-known work is his dictionary about the Duala language.
- Andreas-Martin Selignow (2000). "Johannes Ittmann". In Bautz, Traugott. Biographisch-Bibliographisches Kirchenlexikon (BBKL) (in German). 17. Herzberg: Bautz. cols. 686–688. ISBN 3-88309-080-8.
- unpublished manuscripts and free literature
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