Research into microwave radiation from the Earth’s surface in the presence of vegetation canopies, as well as the development of algorithms for retrieval of soil and vegetation parameters from microwave radiometric measurements, have been actively conducted for the last thirty years by many scientific groups and organizations all over the world. The capability of the microwave radiometric method to determine soil moisture and vegetation biometric indices was revealed a quarter of a century ago by the author and many of his colleagues. In fact, soil moisture and vegetation covers play a key role in the hydrological cycle and in water and energy transfer on the border of land surface and atmosphere through evaporation and transpiration. Accomplishment of large international projects that include global monitoring of the hydrological state of land surface (EOS Aqua, SMOS, Hydros, and others) shows that microwave radiometry of soil and vegetation more and more has become an instrument of practical application and operational use. In this respect, a systematic account of questions concerning the microwave radiometry of the Earth’s surface in the presence of vegetation canopies seems to be useful and is the main objective of the book.