Solution chemistry is carried out in solvents, that is in liquids under the conditions of application, which can exert a considerable influence on the properties of the dissolved solute species. A short historical overview on the influence of solvents on chemical processes (equilibria, reaction rates) and physical processes (absorption spectra, crystallization) is presented. The term “solvent polarity” is discussed, and a solvatochromic parameter for its empirical determination is mentioned. A classification of solvents according to their chemical bonds is given, with special attention to supercritical fluids, fluorous solvents, and room temperature ionic liquids as promising new reaction media.