Book excerpt: The coming generations of wireless network technologies will serve, not only as a means of connecting physical and digital environments, but also to set the foundation for an intelligent world in which all aspects are interconnected, sensed, and endowed with intelligence. Beyond merely providing communication capabilities, future networks will have the capacity to "see" and interpret the physical world. This development compels us to re-imagine the design of current communication infrastructures and terminals, taking into account crucial aspects such as fundamental constraints and tradeoffs, information extraction and processing technologies, issues of public security and privacy, as well as the emergence of numerous new applications. This field of research is known as Integrated Sensing and Communications (ISAC), and it has ushered in a paradigm shift towards the omnipresence of radio devices.This book provides the first comprehensive introduction to the ISAC theoretical and practical framework. Each chapter is authored by a group of world-leading experts, including over 10 IEEE Fellows. Readers can expect to gain both a broad overview and detailed technical insights into the latest ISAC innovations.