The extent of knowledge and practice of contraception in African populations remains hard to evaluate and despite the great influx of data from the World Fertility Surveys, the impact of contraception on fertility levels is difficult to measure. The practice of abstinence for the purpose of spacing births is widespread in Africa. It was discussed in demographic terms already by Lorimer in 1954. More recently the Caldwells (1977, 1981), by carefully investigating the phenomenon among the Yoruba, contributed greatly to establish the place of sexual abstinence in the study of the determinants of African fertility. Lately, data from the World Fertility Survey have shown large variations in the length of post-partum abstinence between countries and among different ethnic groups. Anthropological research has thrown some light on the different functions attributed to post-partum sexual abstinence, and the different reasons for practicing it.