This thesis examines the patterns and determinants of the marriage postponement and fertility decline experienced by Iranian women during the last two decades of the twentieth century. The thesis accounts for temporal changes in the socio-economic context of marriage and childbearing (e.g. improvement in education, urbanisation, economic fluctuations, etc.) and examines the marriage timing and fertility patterns of the cohorts of women who contributed to the recent marriage and fertility changes in order to provide more insight into the demographic behaviour of women with specific life course experiences. A topic of specific interest is the variation between the ethnic groups in Iran. The findings suggest that the recent marriage postponement was related to improvements in women's education and restrictions in the availability of suitable spouses (marriage market), with the former being the only factor contributing to the marriage delay of consecutive (1971-75 and 1976-80) birth cohorts. The recent decline in the probability of second and third conceptions was related to improvements in women's educational level, reductions in child mortality, and improvements in children's enrolment in education. The contribution of son preference to the probability of conception of a second child and the specific impact of urbanisation and industrialisation on the recent marriage and fertility changes were also notable. Different socio-economic factors were found responsible for the decline in the probability of a second conception across consecutive cohorts. of women (those who became exposed to the risk of childbearing in 1986-90 and 1991-95), whereas cohort differences in the probability of a third conception was not generally related to socio-economic forces, probably reflecting a common preference for stopping at two children. The findings also highlight the role of cultural factors associated with ethnicity in shaping differential patterns of marriage timing and suggest that ethnic differences in fertility are strongly related to ethnic differences in socio-economic attributes.