This chapter reviews existing theory and associated research on the development of social networks, and provides an overview of conceptual and methodological issues in the study of social network development. Issues common to research on network development include problems of definition, informant selection, reliability and validity, and setting network boundaries. It also includes the relevance of specific network characteristics, assessing network functions and providers, the effects of personal and contextual factors, the role of cognition, specification of change processes, and articulating network research with other research on the development of social relationships. The chapter presents a brief glimpse of unique trends and emerging work on social networks. This includes work on social network closure, observational studies, specialized populations, cyberspace networks, and interventions. Studies of specialized populations are potentially useful, as they may lead to an understanding of social network development under nonnormative conditions.