This book is a result of a wide collaboration between experts in the field of microwave radiometry and its applications. Originally written as a summary report on the research work by the European Cooperation in Scientific and Technical Research (COST) designated as COST Action 712@ this textbook covers the following topics: radiative transfer and microwave radiometry; emission and spectroscopy of the clear atmosphere; emission and scattering by clouds and precipitation; surface emission; and dielectric properties of natural media. Author Christian M???ler