We study the development of common ground in an emergency management planning task. Twelve three-person multi-role teams performed the task with a paper prototype in a controlled setting; each team completed three versions of the task. We use converging measures to document the development of common ground in the teams and present an in-depth analysis of the characteristics of the common ground development process. Our findings indicate that in complex collaborative work, process common ground increases, thus diminishing the need for acts like information querying or strategy discussions about how to organize the collaborative activities. However, content common ground is created and tested throughout the three runs; in fact dialogue acts used to clarify this content increase over time. Discussion of the implications of these findings for the theory of common ground and the design of collaborative systems follows.