Light is the electromagnetic phenomenon we exploit for remote sensing. Its basic laws concerning the transmission through the interface of two different media are governed by reflection and refraction. Reflection governs the way light is backpropagated and refraction dictates how light is transmitted. Refraction is related to the real refractive index of a medium. Dispersion relates to the way the light of a given wavelength is transmitted. Since light of different wavelengths are transmitted at different angles, the phenomenon leads to the concept of dispersion. These three simple principles are at the core of the understanding technology of remote sensing.