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 establi,shed 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.