Publisher Summary This chapter presents information on relating chromatography to separations. A chromatographic method can be considered simply a physical method of separation, in which components to be separated are distributed between two phases. The chapter discusses both the fundamental aspects and the practical applications of separations, including chromatography, with major emphasis on laboratory- and analytical-scale separations. Small-scale nonchromatographic and chromatographic separations that are commonly used by many chemists and employed in various other areas of science and technology have also been discussed in the chapter to demonstrate the diversity and the unity of separation science. Some of these separation processes that are useful in large-scale industrial applications have been also included in the chapter. Chromatography derives its name from “chroma” and “graphy,” meaning color writing. Chromatography can be defined as “Chromatography is essentially a physical method of separation in which components to be separated is distributed between two phases, one of which does not move (appropriately called the stationary phase) and the other that moves through it in a definite direction (commonly described as the mobile phase).” The two phases in extraction, in technical jargon in industry, are called the “raffinate” and the “extractant.” The stationary phase in chromatography is similar in function to the raffinate in extraction and the mobile phase is equivalent to the extractant. The chapter also discusses several physicochemical phenomena, including equilibrium processes, gas–liquid processes, gas–solid processes, and others.