Electromagnetic moisture measurement technologies have proven to be valuable tools in diverse applications. This monograph covers basic aspects of nondestructive electromagnetic methods of water content determination and relates to the associated highly multidisciplinary field of research and development. It also presents a comprehensive selection of relevant field-tested methods and instruments. The fundamentals of electromagnetic field interactions with dipolar materials are briefly discussed, with special attention towards the dielectric properties of water and aqueous solutions. A tutorial and overview of electromagnetic measurement methods is presented, including dielectric spectroscopy in broad frequency and time domains, as well as dielectric imaging techniques. This review is complemented by a demonstration of successful real-world implementations for the moisture determination of soils, snow, buildings and building materials, food and agricultural goods, as well as various industrial products. The text is completed by a guide concerning the use of reference liquids for the calibration of sensors and instrumentation and by a bibliography of more than 850 references. The monograph is useful as a reference book for researchers and engineers and as a textbook for upper-level students interested in the water content determination of materials.