The Yolngu tribes have a distinctive system of social organisation, which is mirrored by their languages. Each clan (mala) has its own dialect (matha), with the matha being grouped into eight closely-related languages. Within each language, there are two groups of dialects, one associated with the Dhuwa moiety and the other with the Yirritja moiety; there are systematic relationships between the two sets of dialects (in terms of the length of words, etc.). Over thirty three years ago, Bernhard Schebeck made the first definitive study of the Yolngu peoples and their languages, here published for the first time. It has provided the foundation for all later studies of the Yolngu clans, their languages and their social system. There are profiles of the phonological and morphological character of the languages, with discussion of borrowings, and of the recently evolved 'contact language', which has significant simplifications from traditional speech. Schebeck deals in some detail with earlier classifications, by Warner and Berndt. He also provides an analysis of many types of names, including clan names, dialect names, war names and ceremonial names. The author has added a preface and notes, updating the discussions.