Transnational Organized Crime (TOC) or more specifically transnational organised criminal activity is organised criminal activity that involves the crossing of international borders. This chapter examines transnational criminal activities and the criminal collaborations that underlie such activities using a network approach. It provides an overview of the network perspective and introduces social network analysis (SNA). The chapter focuses on the application of the network approach and SNA to flows of transnational illicit commodities, the structure of transnational criminal networks, patterns of criminal collaborations, and key players in transnational criminal networks. SNA is a method for the collection, categorisation, and analysis of the network structure that emerges from the ties between all nodes in a network and the patterns that emerge from the interconnections of actors in networks. TOC requires collaborations between actors, primarily due to the complex nature of activities that need to be undertaken, with such activities often spanning across several different countries.