This paper aimed to study the effect of economic and social factors in the falling off fertility rates throughout the World. The fertility rates all over the world are declining, and many socio-economic factors are seemed to be associated with this decline. The study examined these factors which include: the percentage of contraceptive prevalence, the infant mortality rate, the real per capita income, the female participation in the labour force, the adult literacy rate for males, the adult literacy rate for females, the percentage of the labour force in agriculture, the percentage of population living in urban areas, and the percentage of population with access to health services. On the other hand, and among many fertilities measures we used total fertility rate because it is more likely to be affected by these socio-economic variables than other fertility measures. Based on our data, which were taken from the periodicals of the United Nations, the results showed that, and with the exception of the female participation in the labour force, all variables under study showed an extreme significant association with the total fertility rate. Fertility behavior was shown to be considerably affected by all the variables except the percentage of population living in urban areas and the percentage of population having access to health services. These variables explained almost all the variations in fertility behavior. The percentage of contraceptive prevalence was the most important variable among these variables. Thestudy also represented the original variables in fewer factors using the Factor Analysis technique, with which only two factors were extracted: the first one is strongly related to almost all socio-economic variables and the second is related to the female participation in the labour force. This confirmed the strong association between the socio-economic variables and fertility behaviors.