Cambodia, Indonesia and the Philippines are three out of the four Association of Southeast Asian Nations (ASEAN) countries whose fertility remained above replacement level. Within each country, fertility varies widely across socio-economic sub-groups, resulting mainly from differentials in age at marriage and contraceptive use. Low fertility has resulted in population ageing and labor shortage, giving rise to growing concerns. A better understanding of fertility dynamics is therefore needed to inform policy. This thesis seeks to analyze fertility differentials between Cambodia, Indonesia and the Philippines, and fertility differentials and factors affecting childbearing in each of the three countries. Data for this thesis are taken from the latest Demographic and Health Survey (DHS) in each country under study. DHS covered married women aged 15-49 and collected information on place of residence, couple's education, couple's work status, wealth index, women's household decision-making autonomy, and their attitude towards wife beating by husband. All these were used as predictors of the number of children ever born (CEB). This thesis also studies the association between socio-economic variables and the two main proximate determinants of fertility - age at first marriage and contraceptive use. Bongaarts' model was used to examine the effects of marriage postponement and contraceptive use on fertility. Results from Negative Binomial Regression analysis show that women employed in the non-agricultural sector and wealth index are inversely related to CEB in all three countries after controlling for other variables, women's age and duration of first marriage. Couple's education are negatively correlated with CEB in Cambodia and the Philippines. Disagreeing with wife beating led to fewer children among Indonesian women. The following variables correlate positively with CEB in the multivariate context, which are incongruent with findings from past studies: urbanization in the Philippines, husband's education and employment in Indonesia. Delayed marriage and contraceptive use are the two most important proximate determinants of fertility in all three countries.