This chapter is devoted to recalling a number of results of importance for development in later chapters. Most of these concepts are assumed to be already known to the reader, and those derivations that are missing will be found in textbooks on optics and electromagnetism. The main aim here is to provide a summary of the polarization properties of the simplest electromagnetic wave one can conceive: the monochromatic, time-harmonic, plane wave.

The terms light and electromagnetic wave will be understood as synonymous throughout the text. More specifically, we will be referring to the visible part of the spectrum and its two nearest neighbors, the ultraviolet and the infrared. Many of the topics discussed are also applicable to other wavelength regions. In particular, it is worth noting that radio observations use most of the concepts we shall be developing here for the optical region, although they are not in principle necessary for that wavelength range.