This chapter proposes a way of informing creative design of mobile information systems by acknowledging the value of ethnography in HCI and tackling the challenge of transferring that knowledge to interface design. The proposed approach bridges the gap between ethnography and interface design by introducing the activities of field-data informed design sketching, on a high level of abstraction, followed by iterative development of paper-based mock-ups. The outcomes of these two activities can then be used as a starting point for iterative prototype development— in paper or in code. This is particularly useful in situations where mobile HCI designers are faced with challenges of innovation rather than solving well-defined problems and where design must facilitate future rather than current practice. The use of this approach is illustrated through a design case study of a context-aware mobile information system facilitating people socialising in the city.