Boko/Busa is a cluster of three closely related south-eastern Mande languages or dialects spoken in Benin and Nigeria. The aim of this research has been to describe the phonological, tonological, morphological and grammatical system and processes which occur within the Boko/Busa language cluster, using the approaches of modern linguistics to analyse and present the material. The author, Ross Jones, has had twenty eight years of practical experience with these languages in Bible translation and literacy. As Boko is the major language of the cluster, as well as the most stable and complex, the basic description is of Boko, with variations in the related languages of the cluster, Bokobaru and Busa, being described as they occur. The sources of evidence and authority consist in a thorough set of language examples. Tone is both lexical and grammatical and is an integral part of these languages. Tone changes in verbs and subject pronouns express aspect and mood, while the final tone on NP items differentiates specific from non-specific items. Tone also plays a major role in the complex and pervasive system of logophoricity. The introduction puts these languages in their setting by looking at the ethnography, language classification and historical background, while appendices give lists of lexical material, including an extensive list of loanwords and some sample texts.