This position paper outlines a current research project focusing on the challenges of interaction design for context-aware mobile computer systems. This challenge is approached from a novel perspective on context-awareness; by exploiting knowledge about the user’s context to create indexical user interfaces that carry a major part of their meaning implicitly through the settings in which they are used, thus reducing the need for explicit information representation cluttering the limited screen real estate of mobile devices. The research project aims at creating a theoretical foundation for future research into interaction design with context-aware mobile computer systems and to develop the concept of indexicality as an interaction design principle for such systems. Achieving this, we are conducting a theoretical as well as a technical stream of research involving field studies into the context of mobile computer system use and experimental design, implementation and evaluation of pr...