The basic principles of salt extraction are discussed in a systematic way, both from the theoretical and the practical point of view. The choice of the method of treatment depends on the kind of stone its size, shape and location. The problems concern not only the preservation of stone as material but also of the stone antiquity, which may mean a big difference. A detailed preliminary examination is necessary to learn not only about the state of the stone object but also about its artistic and documentary significance. A preliminary protection of the object before treatment and a consolidation afterwards may often be necessary. The concept of effectiveness of treatment is discussed. A few examples of practical problems of salt removal are included.