In the everyday world, much of what we do as social beings is dictated by how we perceive and manage our interpersonal space. This is called proxemics. At its simplest, people naturally correlate physical distance to social distance. We believe that peoples expectations of proxemics can be exploited in interaction design to mediate their interactions with devices (phones, tablets, computers, appliances, large displays) contained within a small ubiquitous computing ecology. Just as people expect increasing engagement and intimacy as they approach others, so should they naturally expect increasing connectivity and interaction possibilities as they bring themselves and their devices in close proximity to one another. This is called Proxemic Interactions. This book concerns the design of proxemic interactions within such future proxemic-aware ecologies. It imagines a world of devices that have fine-grained knowledge of nearby people and other deviceshow they move into range, their precise distance, their identity, and even their orientationand how such knowledge can be exploited to design interaction techniques. The first part of this book concerns theory. After introducing proxemics, we operationalize proxemics for ubicomp interaction via the Proxemic Interactions framework that designers can use to mediate peoples interactions with digital devices. The framework, in part, identifies five key dimensions of proxemic measures (distance, orientation, movement, identity, and location) to consider when designing proxemic-aware ubicomp systems. The second part of this book applies this theory to practice via three case studies of proxemic-aware systems that react continuously to peoples and devices proxemic relationships. The case studies explore the application of proxemics in small-space ubicomp ecologies by considering first person-to-device, then device-to-device, and finally person-to-person and device-to-device proxemic relationships. We also offer a critical perspective on proxemic interactions in the form of dark patterns, where knowledge of proxemics may (and likely will) be easily exploited to the detriment of the user. Table of Contents: Acknowledgments / Videos / Figure Credits / Introduction / Part I / Ubicomp in Brief / Proxemic Interactions Theory / Operationalizing Proxemics for Ubicomp Interaction / Exploiting Proxemics to Address Challenges in Ubicomp Ecologies / Part II: Exploiting Proxemics in Ubicomp Ecologies / Person/Person-to-Device Proxemic Interactions / Device-to-Device Proxemic Interactions / Considering Person-to-Person and Device-to-Device Proxemics / Dark Patterns / Conclusion / References / Author Biographies.