This monograph is the first study of the acquisition of Swahili as a first language. It focuses on the acquisition of inflectional affixes, with a particular emphasis on subject agreement and tense. Other inflectional affixes are also investigated, including object agreement and mood. The study surveys the adult dialect in question, Nairobi Swahili, discussing social, phonological, morphological and syntactic properties. Data, analyses and copious examples are presented of the naturalistic speech of four Swahili speaking children. The data are tested against six influential theories of child language, and the results show that processing and metrical theories of telegraphic speech fail to account for the observed patterns, while grammatical theories of child language fair significantly better. The data and analyses presented in this book are indispensable for linguists and psychologists interested in the acquisition of inflectional material and other cross-linguistic properties of child language.