Originally published in 1969, this book examines the factors which at different historical periods led people to use one language (Swahili) rather than another, or within a given period, to use a particular language in one set of circumstances. The national language of Tanzania and much of East Africa, Swahili is unique among African languages in its verse literature, which dates back to the 18^th Century and was written in the Arabic script. This book traces the remarkable expansion of Swahili, which was linked with the expansion of trace, missionary activities and the establishment of Colonial administrations and the development of education.