The goal of this paper is to describe the development of an instrument to measure team situation awareness (TSA). Individual team member SA may or may not be shared through communication processes with other team members. Most existing instruments do not measure these processes but measure TSA as a product. Because team members have access to the quality of their communication processes, we developed a self-rating instrument. Advantages, compared to existing TSA instruments, are that it is non-obtrusive with the task and easy to use. Based on a literature review, we selected conditions, processes and outcomes that had to meet three criteria. They had to be relevant for achieving and maintaining TSA, easy to measure, and offer opportunities for team leaders to improve TSA. We administered the instrument in two military and one civilian crisis management exercise. On the basis of these results, we determined psychometric properties such as validity and reliability of the items constituting the instrument. The results of these case studies show that the instrument provides valuable insight to the team leader. The questionnaire will be further improved by developing an automatic tool that identifies and visualizes the feedback on TSA to the team.