This volume is part of an effort to review what is known about the determinants of fertility transition in developing countries and to identify lessons that might lead to policies aimed at lowering fertility. It addresses the roles of diffusion processes, ideational change, social networks and mass communications in changing behaviour and values, especially as related to childbearing. A new body of empirical research is currently emerging from studies of social networks in Asia (Thailand, Taiwan, Korea), Latin America (Costa Rica) and Sub-Saharan Africa (Kenya, Malawi, Ghana). Given the potential significance of social interactions to the design of effective family planning programmes in high-fertility setting, efforts to synthesize this emerging body of literature are important.