This volume addresses the physical foundation of remote sensing. The basic grounds are presented in close association with the kinds of environmental targets to monitor and with the observing techniques. The book aims at plugging the quite large gap between the thorough and quantitative description of electromagnetic waves interacting with the Earth''s environment and the user applications of Earth observation. It is intended for scientifically literate students and professionals who plan to gain a first understanding of remote sensing data and of their information content.