Standards for 5G and beyond will require communication systems with a much more flexible and cognitive design to support a wide variety of services including smart vehicles, smart cities, smart homes, IoTs, and remote health. Although future 6G technologies may look like an extension of their 5G counterparts, new user requirements, completely new applications and use-cases, and networking trends will bring more challenging communication engineering problems. New communication paradigms in different layers will be required, in particular in the physical layer of future wireless communication systems. This comprehensive book is intended to be both a tutorial on flexible and cognitive radio access technologies for 5G and beyond and an advanced overview for technical professionals and managers in the communications industry, as well as researchers in academia and industry. The authors cover enabling radio access technologies for 5G and beyond, not only from a standard specific angle (like 5G) but also by considering future trends beyond 5G. Rather than specific standard implementations, the book covers a wide variety of technologies and their uses. The presentations are both descriptive and mathematical in nature to cater to readers who need mathematical description as well as readers who do not. The book is written at a level suited to readers who already have a background in electrical engineering and basic wireless communications.