The Indexical Interaction Design for Context-Aware Mobile Computer Systems is a STVF funded talent project running from 2004-06 involving researchers from the HCI groups at Aalborg and Melbourne Universities. The project approaches the challenges of mobile interaction design from a novel perspective on context-awareness inspired by the semiotic concept of indexical information representation. The semiotics operates with three types of representations: symbolic (conventional), iconic (similarity) and indexical (material/causal). Symbols and icons are ways of representing information independent of context. Indexes, on the other hand, are ways of representing information with a strong relation to their context and exploiting information present in the interpreter’s surroundings (i.e. signposts and information boards). The idea of applying indexicality to interface design for context-aware mobile computers is that if information and functionality can be indexed to the user's situation, then information already provided by the context becomes implicit and does not need to be displayed. Hence, the user’s environment becomes part of the interface. On the basis of this interfaces can be created 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 Indexical Interaction Design project consists of a theoretical as well as a technical stream of research. This involves field studies into the context of mobile computer system use and experimental design, implementation and evaluation of prototype systems. On the basis of this the project is generating a theoretical foundation for future research into interaction design with context-aware mobile computer systems and developing the concept of indexicality as an interaction design principle for such systems.