Summary. — If demographic and health surveys have underlined declining fertility trends in many countries of sub-Saharan Africa, little is known on the precise timing and the speed of the fertility transition in the continent. This study attempts to fill this gap, by using an innovative approach to the analysis of DHS data and other relevant surveys. The method utilizes fine tuning of fertility trends year by year, for urban and rural areas separately. The paper starts by a case study of the fertility transition in Kenya. The same method is later applied to more than 20 countries. Results indicate that in many countries, fertility started to decline in the late 1960s and 1970s in urban areas, and about 10 years later in rural areas, much earlier than usually thought. Placing a time frame at the onset of the fertility transition allows one to develop further analysis of the key determinants of the fertility transition. Emphasis is on the role of family planning programs, as well as on emerging independent individual behavior such as delayed marriage and induced abortions. Comparison is made with the situations of other developing countries, and with the possible role of mass media, in particular television