This book addresses two of the most important questions in modern African history: the causes of rapid population growth, and the origins of the HIV pandemic. It examines three societies on the Uganda-Tanzania border whose distinctive histories shed new light on both of these phenomena. This was the region where HIV in Africa first became a mass rural epidemic, and also where HIV infection rates first began to decline significantly. Before HIV argues that only by analysing the long history of changes in sexual behaviour and attitudes can the shape of Africa's regional epidemics be fully understood. It traces the emergence of the sexual culture which permitted HIV to spread so quickly during the late 1970s and 1980s back to the middle decades of the twentieth century, a period when new patterns of socialization and sexual networking became established. The case studies examined in this book also provide new insights into the relationship between economic and social development and trends in fertility and mortality during the twentieth century. These three societies experienced the onset of rapid population growth at different moments and for different reasons, but in each case study area the key mechanisms appear to have been a decline in child mortality, a shortening of birth intervals, and a marked decline in primary and secondary sterility.