This chapter shifts the attention to social networks and starts with discussing the problem of creating and maintaining trust, which was a major obstacle to long-distance trade and cross-cultural interaction in the ancient world. It introduces key terminology from New Institutional Economics before moving on to discussing trade diasporas as forms of social networks. Janet Landa’s work on Ethnically Homogenous Middlemen Groups and clublike organizations as solutions to the problem of trust is outlined, and its applicability on ancient evidence is argued on cases drawn from the forensic orations of Demosthenes (fourth century BCE) as well as on evidence of religious and professional associations in the ancient Mediterranean, West Asia and South Asia.