This textbook covers the integration of wireless communications and radar sensing (ISAC), tackling some of the major technologies in 6G wireless networks. The book provides a comprehensive introduction to communications and radar, complete with the most updated and significant research topics. The author then introduces four aspects of ISAC: (a) the introduction to communications and sensing; (b) system design of ISAC; (c) networking of ISAC; (d) applications. The book features an in-depth tutorial for the areas of communications and radar and a comprehensive survey for ISAC. The author covers results intensive research and successful application in communities of wireless communications, radar, remote sensing, and computer engineering. The book can be used to shape the current research paradigm and cause impact on the standard of 6G systems.