A central challenge in interaction design has to do with its diversity. Designers, engineers, managers, marketers, researchers and users all have important contributions to make to the design process. But at the same time they lack shared concepts, experiences and perspectives. How is the process of design-which requires communication, negotiation and compromise-to effectively proceed in the absence of a common ground? I argue that an important role for the interaction designer is to help stakeholders in the design process to construct a lingua franca. To explore this issue, which has received remarkably little attention in HCI, I turn to work in urban design and architecture. I begin by discussing a case study in community design, reported by Hester [10], that demonstrates the power of a lingua franca for a particular design project. I then describe the concept of pattern languages and discuss how they might be adapted to the needs of interaction design in general, and used, in particular, as meta-languages for generating lingua francas for particular design projects.