Coal is cleaned industrially by freeing the occluded mineral impurities and physically separating the coal and refuse particles on the basis of differences in density, settling characteristics, or surface properties. While physical methods are very effective and low in cost when applied to the separation of coarse particles, they are much less effective when applied to the separation of fine particles. Also they can not be used to remove impurities which are bound chemically to the coal. These deficiencies may be overcome in the future by chemical cleaning. Most of the chemical cleaning methods under development are designed primarily to remove sulfur from coal, but several methods also remove various trace elements and ash‐forming minerals. Generally these methods will remove most of the sulfur associated with inorganic minerals, but only a few of the methods seem to remove organically bound sulfur. A number of the methods employ oxidizing agents as air, oxygen, chlorine, nitrogen dioxide, or a ferric salt to oxidize the sulfur compounds to soluble sulfates which are then extracted with water. The sulfur in coal may also be solubilized by treatment with caustic. Also sulfur can be removed by reaction with hydrogen at high temperature. Furthermore, it is possible to transform the sulfur bearing minerals in coal to materials which are easily removed by magnetic separation.