ROADMAPPING EXTENDED REALITY This book offers a comprehensive overview of the technological aspects of Extended Realities (XR) and discusses the main challenges and future directions in the field. This book is important and timely - XR technologies have overcome the 3 main aspects that were holding it back from mainstream adoption: cost, cables, and size. However, there are many aspects of XR technologies that are now going to be explored and developed that still need urgent research in terms of security, privacy, health and safety, long-term effects, addiction risks, and age-related developmental concerns, and the aim of the book is to inform all readers of these open issues and challenges. There are currently a great number of interdisciplinary researchers and developers working in the XR R&D field. Recently, XR technologies moved from the Gartner Hype Cycle onto the Plateau of Productivity on the Gartner Hype Cycle signaling that the fundamental XR technologies are now deemed mature technologies and ready for deployment in a wide variety of application areas. Corroborated by the fact that XR technologies are part of the future Metaverse, a concept that went rapidly mainstream during the time of writing of this book. Roadmapping Extended Reality is divided into two parts: (1) fundamentals and (2) applications. The first part covers the main technological aspects of XR. The chapters in this section review and discuss relevant fundamental concepts of XR, the actual state-of-the-art, and future challenges. The second part of the book focuses on covering a wide range of applications of XR including a future roadmap. All in all, the book offers a snapshot of the state-of-the-art in XR and addresses the needs of a multidisciplinary audience working in both academia and the industry, as well as stakeholders at government agencies and non-profit organizations. Audience This book is aimed at academic and industrial developers, exploring and developing applications in the XR, VR, AR, AI, smart IoT, 4th Industrial Revolution space, including those that are solving technology requirements, human factors, evaluation methodology advances, and ROI investigations.