Book excerpt: Design for Emergence investigates spontaneous, unpredictable uses of technology that are driven by social contexts and collaborative processes, based on our ability to communicate our presence, both virtual and physical, in symbolic ways. In light of the fact that social dynamics and unexpected uses of technology can inspire innovation, this book proposes a research model of design for emergence, focusing on emergent phenomena as part of an iterative design process. By providing playful, technology-mediated experiences with minimal structure, unpredictable user behaviours can emerge through exploration, resulting in a richer and more complex, social experience. The research methodology is practice-based; two interactive prototypes were designed, implemented and evaluated in different contexts: an online multiplayer BumperCar game and a wireless, location-based urban game of 'tag', called CitiTag. User studies showed that collaborative, spontaneous play can enhance the sense of social participation in a group activity. Collective and individual behaviours and creative uses of technology emerged from a simply designed application based on symbolic presence, both in the virtual and the physical world. CitiTag experiments showed that virtual elements in a mixed reality game can instigate novel experiences in the context of our everyday physical and social environment, with often unexpected results. The observed emergent behaviours are personal and collective extensions of the virtual experience in the real world. The book concludes with a positive view of ubiquitous and social computing, in which the virtual world becomes a 'first class citizen' rather than a substitute for the real world, creating new situations and engaging experiences in the setting of our daily life that were not possible before.