This book offers comprehensive, practical guidance on RF propagation channel characterization at mmWave and sub-terahertz frequencies, with an overview of both measurement systems and current and future channel models. It introduces the key concepts required for performing accurate mmWave channel measurements, including channel sounder architectures, calibration methods, channel sounder performance metrics and their relationship to propagation channel characteristics. With a comprehensive introduction to mmWave channel models, the book allows readers to carefully review and select the most appropriate channel model for their application. The book provides fundamental system theory accessible in a step by step way with clear examples throughout. With inter- and multidisciplinary perspectives, the reader will observe the tight interaction between measurements and modeling for these frequency bands and how different disciplines interact. This is an excellent reference for researchers, including graduate students, working on mmWave and sub-THz wireless communications, and for engineers developing communication systems.