A viable model of interactive discourse must explain how interlocutors share conversational control to construct the discourse, and recognize the contributions of others to it. In my work I focus on one mode of collaboration. I am implementing a system called the Interactive Disourse Planner (IDP) that plans text to describe and justify domain plans interactively. As a testbed for my model, IDP discusses driving routes as the domain plans. In this collaborative mode, the system is the primary speaker and the user is the primary listener. IDP is responsible for planning text to describe and/or justify a domain plan, and the user is responsible for providing feedback that lets the system know how to extend the discussion in a way that is helpful.