This book deals with the sensing of sheet products for a variety of properties including dimensions, moisture, electrical properties and curing state, among others, through the use of open microwave resonators. Starting with an introduction on the ideas and tools needed, the book proceeds through the whole design process, including simulation, experimentation, prototyping and finally testing a complete system. One of the goals of the book is to present a coherent and entirely practical approach to the design of open resonator microwave sensors.