This book has a modest purpose. Many history students interested in Africa wish to study the HIV/Aids epidemic but are hampered by the lack of an introduction to the detailed literature. This book is intended as an introduction, for students and other readers.

The book is not a work of research. A thorough history of the epidemic during its first thirty years would demand fieldwork in affected communities, interviews with those involved, and study of unpublished records of international organisations, national governments, and private individuals. I have not attempted any of these, nor have I the necessary medical and anthropological skills. Instead, the book is a synthesis of the more important and accessible published material, put into a historical form.

A historical account offers four advantages. First, it suggests an answer to the question posed most provocatively by President Mbeki of South Africa: why has Africa had a uniquely terrible HIV/Aids epidemic? Mbeki attributed this to poverty and exploitation. Some earlier analysts suggested that Africa had a distinctive sexual system. This book, by contrast, stresses historical sequence: that Africa had the worst epidemic because it had the first epidemic established in the general population before anyone knew the disease existed. Other factors contributed, including poverty and gender relationships, but the fundamental answer to Mbeki's question was time. Like industrial revolutions or nationalist movements, Aids epidemics make sense only as a sequence.

Second, a historical approach highlights the evolution and role of the virus. Because HIV evolves with extraordinary speed and complexity, and because that evolution has taken place under the eyes of modern medical science, it is possible to write a history of the virus itself in a way that is probably unique among human epidemic diseases. At the same time, the distinctive character of the virus - mildly infectious, slow-acting, ineradicable, fatal - has shaped both the disease and human responses to it.

Third, many aspects of the epidemic come into focus only when seen in the longer context of African history. Although HIV/Aids was profoundly different from earlier African epidemics, it arose from the human penetration of the natural ecosystem that is the most continuous theme of the African past.