In a Multiple User Interfaces (MUI) context, several models must be defined and adapted (tasks, user, .). Abstract models are progressively enriched in concrete models using pattern libraries and filtering processes. In this paper, we define the central role of the interaction model in MUI design and specification. This model manages the interaction between the user and the application, and ensures the link between task models, interfaces and the functional core of the application. In our approach, we use AMF, a multi-agent and multi-facet architecture, to define the interaction model. We describe the structure and behavior of an AMF-based interactive system that provides multiple user interfaces. Keywords Multiple User Interface, design patterns, model-based, AMF, XML based language.