Bibliography: pages 208-219. / The Auxiliary is a sadly neglected field of study in Southern African languages. The study investigates the syntactic and semantic behaviour of Auxiliaries in Sesotho. Having established that there is a category AUX in Sesotho, we then developed a descriptive framework in which auxiliaries in Sesotho participate. In this framework we posit as basic the three grammatical-semantic categories of verb phrases, namely, Tense, Aspect and Modality. The next major step was to develop formal tests which we used as defining characteristics for auxiliaries. We had to do this because the formal tests developed for English, for instance, do not work for Sesotho. The data used in this study represents samples of Sesotho as spoken by the native speakers. This work makes contributions in two areas. First, to language studies in Southern Africa and then to general linguistic theory. Since Tswana, Northern Sotho and Southern Sotho form one language group predict that the formal 'tests' we have suggested can be applied in the two Sotho languages as well. As far as Aspect, Tense and Modality are concerned, it is where this study makes a major contribution. Nowhere in Sesotho grammatical studies has either a tense or aspectual system of Sesotho been suggested or discussed. Modality has not even been referred to. In this regard the study is breaking new ground. We hope that a fresh debate will be initiated leading to vibrant discussions on comparative work. A number of studies on syntactic typology have been made. This study affords Sesotho its rightful place in the AUX debate.