The fundamentals of solar energy and PV technology are discussed in this chapter, highlighting their relevance to renewable electricity generation. Solar energy, PV conversion, spectral response, and atmospheric factors influencing PV performance are initially commented on. Special focus is given to the soiling phenomenon, responsible for a significant reduction of PV modules power; its causes, spatial and temporal variability, and the typical composition of the residues are analyzed. The chapter also reviews methods for measuring, modeling, and quantifying soiling losses, as well as mitigation strategies such as manual cleaning, automatic washing, and hydrophobic coatings. Finally, the importance of continuous monitoring and preventive maintenance to maximize PV efficiency is discussed, highlighting some of the main metrics used to measure soiling effects on PV electrical performance.