This thesis aims to identify periods of fertility transition and to investigate determinants of fertility change in Mongolia during the period 1960-1998. Three distinct periods of fertility change have been identified: a) pre-transiton-1960-1975; b) the onset of transition-at around 1975; and c) transition-1976-1998. The latter has split into two periods; socialist and marked economy. This study has found that Caldwell's intergenerational theory, and Cleland's and Wilson's demand theory of fertility transition might fit for Mongolia during the pre-transition period, while Coale's theory of reasons of the decline in marital fertility might apply to Mongolia during the period 1975-1989. Inadequate parental incomes, the disappearance of many social services and people's developing awareness of individualism and self-fulfilment during the shift from a centralized planned economy to a market economy led to conclusion that economic and ideational theories of fertility change might apply to Mongolia during the period 1989-1998. Demographic factors have affected women's childbearing significantly during the last three decades. Forces other than economic prosperity were important in driving the fertility decline during the period of socialist rule. Since the move towards a market economy, economic activity has been a driving force in fertility decline. Age of women, marriage duration, couples' attitude to family planning and women's employment status are potential predictors of the contraceptive use. Mongolian women tend to use IUD and traditional methods. Significant variation exists between primary sampling units in using any form of contraceptive and in choosing IUD against traditional methods.