This paper applies the original and the extended version of Bongaarts' models of the proximate determinants of fertility as a means of pulling together three of the proximate determinants (marriage, contraception and breast feeding). The Demographic and Health Surveys data are used to investigate the changes within and between the countries in order to determine the extent of fertility change and fertility-inhibiting factor(s) most responsible for change.The result shows fertility has been declining in Botswana and Zimbabwe and has just begun in Zambia. Although currently breastfeeding is the major factor for the depressed fertility in all countries, the effect of modern contraception appears to be the major factor behind the fertility decline. There is also evidence to suggest the delayed marriage is assuming a significant role in the fertility transition, particularly in Botswana.