'Vacuum electronic devices are marvels of technology that achieve amazing performance advantages by a sophisticated combination of a vast diversity of physics, materials, components, and engineering principles. This book finds a worthy value-add role in the pantheon of great vacuum electronics (VE) literature by masterfully marrying a comprehensive treatment with carefully crafted choices of appropriate - but not excessive - depth. Thus it informs, provides rigor, but is extremely accessible to many levels. The background treatment of electromagnetics is especially noteworthy - with its mapping of structure properties to equivalent circuit models - since the start for understanding VE is the science and design principles of electromagnetic fields in waveguides and resonators. The coverage of VE devices and critical materials is current and state-of-the-art, which is important since research discovery advances keep pushing the limits of the performance capabilities of modern VE. I wholeheartedly recommend this book.' John H. Booske, University of Wisconsin, Madison