PIP: Paper based on data generated by the World Fertility Survey in 8 countries: Bangladesh, Indonesia, Sri Lanka, Jordan, Peru, Guyana, Colombia, and Panama. The authors address the following issues, among others: the prevalence and duration of breastfeeding; variations in the duration of breastfeeding among different subgroups, classified by age, parity, woman's education, etc,; the key determinants of breastfeeding; and the effect of breastfeeding on fertility. The large majority of women in all the countries breastfed their last 2 children, the number who did not ranging from 2 to 18%. Duration ranged from 9 months (Panama) to 29 months (Bangladesh). Key determinants were women's education, place of residence, husband's occupation, and survival status of the child--consistent for all 8 countries. Women with more education and those living in urban areas breastfeed for shorter periods. Sex of child, age and parity of mother, and mother's work experience showed no independent effect on duration of breastfeeding. Although breastfeeding is not used for family limitation, the possibility that it is used to prolong birth intervals cannot be ruled out. Average length of last closed birth interval increased with prolonged breastfeeding in all 8 countries. 1 month of breastfeeding adds an average of 0.4 months to the birth interval, although there was considerable variation among the countries. To what extent these variations may be due to differences in reporting errors or to other factors could not be determined.