In this paper we extend transactive memory systems (TMS) theory to develop an understanding of the distributed coordination of expertise in high-reliability organizations. We illustrate our conceptual developments in a study of emergency management and response in Greece. We focus on the interaction between operators/dispatchers, ambulance crew, and specialist doctors, including the information and communication technologies (ICT) they use to respond to emergency incidents. Our case contributes to an in-depth understanding of the ways in which high-reliability organizations can sustain a distributed coordination of expertise over the duration of emergency incidents. This is achieved through the cultivation of TMS during a socialization and training period, the dynamic development of trust in emergent actions, and a commitment to shared protocols, which allow for improvisation and bricolage during unexpected incidents. Our findings also explore the role of ICTs in inscribing TMS in computerized protocols, while mediating the development of trust across the team, as well as mediating the construction of running narratives, which enable leaders to coordinate expertise in unexpected incidents.