Bentonites and their majör clay mineral smectites have been among the more important industrial raw materials. Some of the applications are paint, paper, plastics, decolorization, Chemical carriers, liquid barriers, foundry bondants, drilling fluids, desiccants, sealants, cosmetics, adhesives and catalysts. The purification and physicochemical modifications of püre smectites have a great importance to prepare some high technology materials such as pillared clays, organoclays, and polymer/smectite-nanocomposites. In this paper, besides general properties of bentonite, crystal structure, swelling, porosity, surface area, surface acidity, and ion exchange properties of smectites were discussed.