Team decision-making (TDM) is composed of many activities. One important aspect of TDM is information seeking, particularly collaborative information seeking (CIS). Within CIS research, the role of team cognition and the development of team mental models (TMMs) have not been well-studied. In this paper, we examine the development of TMMs during CIS activities. Utilizing qualitative knowledge elicitation methods, we conducted an exploratory laboratory-based study of student teams working on CIS tasks. We report on how the teams describe TMM development, the teamwork and taskwork aspects of the TMM, and the attributes supporting TMM development. The results highlight that the process of TMM development during CIS is similar to TMM development research reported in other studies. Furthermore, to the best of our knowledge, this is the first research to attempt to understand the role of team cognition in CIS and describe the development of a TMM specific to CIS.