It is one of the most commonly used techniques for the purification of solid organic compounds.

Principle:- It is based in the difference in the solubilities of the compound and the impurities in a given solvent. The impure compound gets dissolved in the solvent in which it is sparingly soluble at room temperature, but appreciably soluble at higher temperature. The solution is concentrated to obtain a nearly saturated solution. On cooling the solution, the pure compound crystallises out and is removed by filteration.

For example, pure asprin is obtained by recrystallising crude aspirin. Approximately 2-4 g of crude aspirin is dissolved in about 20ml of ethyl alcohol. The solution is heated (if necessary) to ensure complete dissolution. The solution is then left undisturbed until some crystals start to separate out. The crystals are then filtered and dried.