The function of groups as information processors is increasingly being recognised in a number of theories of group cognition. A theme of many of these is an emphasis on sharing cognition. This paper extends current conceptualisations of groups by critiquing the focus on shared cognition and emphasising the distribution of cognition in groups. In particular, it develops an account of the distribution of one cognitive construct, mental models. Mental models have been chosen as a focus because they are used in (...) a number of theories of high level cognition from different areas of research such as cognitive science and human factors and so the implication of this development is wide reaching. This paper reviews the unconnected literatures on distributed cognition and mental models and integrates them in order to extend the theory of mental models to distributed cognitive systems such as groups. The distributed cognition literature is reviewed and the importance of considering the group as single cognitive system is adopted. A range of mental model theories are reviewed leading to the conclusion that they all have, in some form, the central feature of a mapping onto the cognitive system. Combining these two ideas, it is proposed that the model can be a mapping onto the whole group, if the information is distributed appropriately and the connections between parts of the model maintained through communication. This cognitive construct is referred to as a distributed mental model. Implications and applications of this theory are discussed. (shrink)