This chapter examines social network theory and its application to economic cluster development. The analysis traces the evolution of network concepts—including nodes, ties, centrality, clustering, homophily, and structural holes—and connects them to economic geography’s relational turn. The analysis demonstrates how social networks conduct knowledge flows, innovation, and social capital formation within industrial clusters. Drawing on studies from Silicon Valley, Chile, Sydney, and the UK, the chapter shows that network structure shapes economic outcomes through coordination, trust, and information exchange. This concludes by introducing social network analysis (SNA) as an underutilized but powerful tool for economic development planning.