This essay examines the role of ‘trust’ and cooperation in early modern long-distance trade. While most literature on the subject posits trust as a given attribute of long-distance merchant communities and not as a factor in need of historical explanation or analysis, this essay seeks to provide a historical explanation for the creation and role of trust in such communities. It focuses on the history of Armenian merchants from New Julfa, Isfahan, during the seventeenth and eighteenth centuries. The central theoretical model this essay relies upon to explain trust among Julfan Armenian merchants derives from ‘social capital’ theory as elaborated in sociology and economic sociology, as well as theory from the New Institutional Economics associated with the influential work of Avner Greif. Unlike the latter body of work, however, this essay argues that Julfan trust must be understood not solely as an outcome of informal institutions such as reputation-regulating mechanisms discussed by Greif in his work on Maghribi Jews of the medieval period, but also as a result of the simultaneous combination of both informal and semi-formal legal institutions. In the Julfan context, the essay thus focuses on a merchant arbitrage institution known as the Assembly of Merchants, which enabled Julfan merchants to generate and maintain trust, trustworthiness and uniform norms necessary for collective action and cooperation.