Key Technologies for the 6G Air Interface is an up-to-date reference, providing comprehensive, systematic, and in-depth descriptions of the enabling technologies for the 6G air interface. It includes recent advances, potential future developments, and associated specifications and standards. Simulations and quantitative analyses are used to provide a comprehensive understanding of the performance potential of candidate technologies and their implementation impacts. Recent breakthroughs in fields such as information theory and multi-antenna technology are explained which enables readers to grasp the potential major technology revolution expected for the 6G air interface. Researchers working toward the 6G time frame, industry analysts, governments, and investors monitoring the migration of the mobile industry from 5G to 6G will gain insights from the discussions of the rapid technological developments that are expected, the challenges, the potential for future applications and opportunities, and the balance of innovation and feasibility.