Shared mental models theory normally takes the individual as its unit of analysis. This paper proposes a theoretical framework for studying shared mental models in which the model is considered to be distributed amongst the team. From this framework a cognitive process is predicted which describes how shared mental models are run. A team reasoning task requiring planning was used to illustrate this framework and test predictions derived from it. Two aspects of sharing mental models were studied; the degree of overlap between team members' mental models and the organization of the division of the model between team members. Experimental results showed that the cognitive processes used were distributed amongst the team and support was found for most, but not all, aspects of the proposed process of running a shared mental model. The organization of sharing was found to influence this process.