The advancement of field-based research in development economics has enabled researchers to address challenges associated with identifying the effects of endogenously formed social networks. This keynote will examine how knowledge about social networks can be used to enhance program effectiveness, optimize intervention outcomes, and understand spillover effects of programs and policies. Drawing on examples from recent randomized field experiments, it will discuss the issues regarding causal effects of social networks using RCTs and how researchers can employ social network surveys and experimental manipulations for program evaluation.