Interruptions are common in joint activities like conversations. Typically, interrupted participants suspend the activity, address the interruption, and then reinstate the activity. In conversation, people jointly commit to interact and to talk about a topic, establishing these commitments sequentially. When a commitment is suspended, face is threatened and grounding disrupted. This article proposes and tests a model for suspending and reinstating joint activities, using evidence from naturally occurring suspensions in the Switchboard corpus (Study 1) and from a laboratory experiment (Study 2). Results showed that long suspensions led to more politeness and more collaborative effort in reinstatement than short suspensions. Also, listeners were more polite than speakers in suspending joint activities. Overall, suspending and reinstating a joint activity was shown to be a collaborative task that requires coordination of both the topic and the participants' face needs. (Contains 6 footnotes, 4 excerpts, 1 table, and 3 figures.)