In this work, the authors present a comprehensive coverage of the URLLC including the motivation, theory, practical enablers and future evolution. The unified level of details provides a balanced coverage between its fundamental communication- and information theoretic background and its practical enablers, including 5G system design aspects. The authors conclude by offering an outlook on URLLC evolution in the sixth-generation (6G) era towards dependable and resilient wireless communications. This is the first book to give the reader a complete, yet concise, introduction to the theoretical and application oriented aspects of a topic at the core of both 5G and 6G wireless communication systems. As such, it is essential reading for designers and students of such systems.