The present volume presents the so far unpublished manuscripts by Roland C. Stevenson on Tira and Otoro, two Kordofanian languages spoken by 40,000 (as of 1982) respectively 10,000 speakers (as of 2001) in the Nuba Mountains of central Sudan. Roland C. Stevenson was born in Romford in Essex, England in 1915. He first went to the Sudan in 1937 to work with the Church Missionary Society. From that time on, almost until his death in 1991, he devoted his life as a missionary and linguist to the study of the languages of the Nuba Mountains. His best-known contribution to African linguistics is his PhD dissertation, presented at the School of Oriental and African Studies (SOAS), University of London, in 1951. It was partly published in the journal Afrika und Übersee, vols. 40-41 (1956, 1957) under the title A survey of the phonetics and grammatical structure of the Nuba Mountain languages, with particular reference to Otoro, Katcha and Nyima. He also supplied the data for sections on the languages of the Nuba Mountains in Part 3 of the Handbook of African Languages by A.N. Tucker and M.A. Bryan, The Non-Bantu Languages of North-Eastern Africa (1956), and ist companion volume Linguistic Analyses (1965). Much of his work, however, has remained unpublished. After his death, his family expressed the wish that his papers should be preserved and made accessible to the scholarly community. Among the Stevenson papers, the present manuscript grammars are of 1942 (Tira) respectively 1943 (Otoro). In many branches of science, including linguistics, a manuscript of that time would be obsolete and of interest only to the history of science. Not so in this case. Except for the extracts that found their way into Stevenson's thesis and Tucker and Bryan's Handbook, the data and analyses presented here for the first time in print are genuine and novel additions to our knowledge.