Abstract. An activity is inseparably bound up with time, and interdependent cooperative activities thus need to be coordinated in time. The nature of time is therefore an ever-present issue in the design of computer systems supporting coordination. Based on Activity Theory this paper defines the concept of Temporal Coordination. Then, based on in-depth studies of the socio-temporal aspects of coordinating cooperative work at hospitals, the paper explores this notion of temporal coordination. This analysis identifies some of the highly intertwined temporal problems, constraints, interests, and conflicts, which arise when work subject to temporal limits is to be coordinated. The paper then introduces the PATIENT SCHEDULER, which is a prototype designed during this project to illustrate how aspects of temporal coordination can be supported by computer technology.