Collaborative information‐seeking (CIS) tasks, such as holiday planning, academic research, medical/health information seeking, cannot be tackled without making sense of the task and the encountered information together with collaborators, that is, collaborative sensemaking. In CIS, collaborative sensemaking is an important but understudied aspect. A thorough understanding of collaborative sensemaking behavior in CIS tasks is essential to develop tools to support collaborative sensemaking activities in CIS. In this article, we investigate the general patterns and differences in collaborative sensemaking behavior in travel planning and topic research tasks using the data from 2 observational user studies. The results show the common stages of the collaborative sensemaking process and the differences in users' collaborative sensemaking strategies and activities between the 2 tasks. This comparative study enhances our understanding of the collaborative sensemaking process in CIS tasks and the differences in user's sensemaking behavior according to tasks, and describes implications for supporting collaborative sensemaking behavior in CIS tasks.