This chapter describes modern analytical separation science. It also describes purification procedures known as recrystallization and distillation. The chapter discusses the separation techniques of extraction and chromatography. Distillation of water to remove hardness minerals is an example and probably the most common application in an analytical laboratory. One popular method of separating an analyte species from a complicated liquid sample is the technique known as “liquid-liquid extraction” or “solvent extraction.” In this method, the sample containing the analyte is a liquid solution, typically a water solution, that also contains other solutes. Just one extraction performed on a solution of a complicated sample will likely not result in total or at least sufficient separation of the analyte from other interfering solutes. As with the liquid-liquid examples, the extract is then analyzed by whatever analytical technique is appropriate — atomic absorption for metals and spectrophotometry or gas or liquid chromatography for organics.