Pakistan is a country facing relatively high rates of population growth due to high fertility and decline in mortality rates. This is not only depleting scarce resources but also contributing significantly to environmental degradation. It is, therefore, desirable to know; why fertility rates in Pakistan remain high despite the nationwide family planning coverage since 1965? The objective of this study, therefore, is to establish trends and patterns of fertility among different ethnic groups (on the basis of languages spoken) in Pakistan. The study also explores the major reasons for different fertility behaviour. This is because; there are variety of languages spoken throughout the country having distinct norms, traditions and other customs which directly or indirectly influence fertility and fertility related decisions. The study found that the Balochi or Brohi speaking women had the most children, Sindhi and Pushto speaking women are the women with the second highest fertility levels, Punjabis with the lowest and Urdu speaking almost matching them. The study attributes the high fertility levels among some ethnic groups to low level of education, lower age at first marriage, higher demand for children and greater value placed on number of children. It is also found that fertility levels are high among those ethnic groups who have little knowledge and less use of contraceptives. On the basis of findings, study provides guideline to policy-makers, planners and family planning personnel’s for policy formation to facilitate reduction of fertility in particular context and to target specific sub-groups of population.