In this article we first provide a brief introduction into social network analysis, focusing on the measures and approaches that are used in the empirical contributions in this special issue. Second, we discuss the role of social networks in new product development. Social networks are inherently multilevel; we consider four "levels": networks inside a firm, networks that cross firm boundaries, networks between firms, and networks that reside outside of the firm. Third, we discuss these four levels and highlight some of the extant research. We summarize and position the eight papers in this special issue along these four levels. Together, we argue, these papers provide an interesting coverage of this burgeoning field.