'An initial interest in research into mobile context-aware user interfaces motivated a study of current scientific literature within the field. The study revealed a gap in research into development of HCI design principles, and this in turn motivated us to make research into development of HCI design principles the subject of this thesis. The theoretical concept of indexicality is promising in relation to mobile context-aware user interfaces and it was chosen as foundation for the development of design principles. A set of provisional design principles was evaluated in a field study of a system that supported using public transport in an urban environment. A mobile context-aware system was developed for the evaluation and the user interface was designed by applying the design principles in an indexical analysis of the use domain of the case. Furthermore, a user requirements study was carried out in order to identify user requirements. The evaluation validated the design principles. Furthermore, we found that a push strategy for delivering information to the user appeared to work well in a context-aware interface such as this. '