This book introduces Zynq Ultrascale+ RFSoC, a technology that brings real, single-chip, Software Defined Radio (SDR) to the marketplace. RFSoC devices are the first adaptive SoCs (Systems-on-Chip) to monolithically integrate multiple RF signal chains along with Arm application and real-time, multicore processors and programmable logic. By eliminating the need for dozens of discrete devices, RFSoC chips offer unprecedented flexibility and reduced power consumption when compared to alternative, multi-component solutions. RFSoC is not so much a radio on a chip, but almost an entire base station on a chip! Moreover, besides widespread application in 5G mobile communications, RFSoC devices also enable the design and development of emerging 6G systems and are now being used in many other domains including high-speed radar, advanced instrumentation, radio astronomy and quantum computing. We anticipate that the book will be of interest and use across a number of technical areas. It serves as an introduction to the family of RFSoC devices and its key features and programmability. Special attention is paid to the RF signal chains including the high-resolution, direct RF data converters, the digital up-converters and digital down-converters, and the quadrature mixers. Further sections explore the Forward Error Correction (FEC) units and the interfaces between the RF, programmable and the processor subsystems. The book explores software defined radio concepts and architecture and key DSP algorithms such as multi-Nyquist zone operation, frequency planning, multi-rate FIR filters and FFTs. By integrating high-bandwidth, high-resolution, direct-RF, analogue-to-digital and digital-to-analogue converters, RFSoC devices can access more of the electromagnetic spectrum than any previous SoC. Whatever signal bands are of interest to you, RFSoC technology provides a programmable platform for innovative research and design! A selection of hands-on exercises via Jupyter Lab notebooks accompany the book and are available from the book's companion GitHub repository. There are also design examples (including SDR designs) to build and implement real systems based on PYNQ (Python open-source, design framework) and supported boards, such as the RFSoC4x2. Wherever you are in your career, whether you are a student, a researcher, an educator, a professional engineer or manager, we hope that you find this book a useful and pragmatic reference on the incredible RFSoC technology.