The knowledge of physical laws and principles regulating the emission of e.m. radiation and its interactions with the matter, as well the ones related to the design, setting-up and control of EO platforms and related instruments, are of paramount importance for a right interpretation of EO measurements in relation with the investigated Earth's phenomena and parameters. The most important physical fundaments regards: the theory of electromagnetic waves propagation described by the Maxwell's equations, the theory of e.m. radiation and of its interaction with the matter, the methods and instruments for e.m. radiation measurement and/or generation, the fundamentals of thermodynamics and of mechanics. As far as Earth Observation is concerned, further, specific topics have to be addressed which are related to: spectral-specific matter-radiation interactions, natural (e.g. Earth, Sun) and artificial (e.g. MW) sources of e.m. radiations, atmospheric physics and radiative transfer equations, basic physics of e.m., optical and MW, sensors and sources, theory of satellites orbits, theory of rockets, physical fundaments of interpretation of optical and MW data collected by passive and active techniques.