This paper examines, theoretically and empirically, the impact of reproductive externalities on fertility behaviour in Kenya. We examine this issue by identifying structural forms of social interaction operating across individuals belonging to di§erent ethnic groups on the number of children ever born. We use the 1998 Demographic and Health Survey data on 5994 women from Kenya to examine whether the ílocalíe§ect of household-level ináuences, cluster-level residential settlement, and the more íglobalí e§ect of ethnicity, is important over and above an individual's characteristics in order to explain variations in fertility behaviour in this country. In so doing, we conclude that the importance of social interactions for fertility is that it may be necessary to target population policy towards varied ethnic groups in di§erent ways, with relevance for population policy in ethnically pluralistic societies more widely