Abrasives are hard substances used in various forms as tools for grinding and in other surface finishing operations. They are able to cut materials too hard for other tools and give better finishes and hold closer tolerances than can be obtained economically by other means on most materials. The important properties of an abrasive material are: (1) hardness, (2) toughness, (3) resistance to attrition, and (4) friability. A grinding wheel is made of abrasive grains held together by a bond. Grinding is done on surfaces of almost all conceivable shapes and materials of all kinds. It may be classified as a non-precision or precision process, according to purpose and procedure. Non-precision grinding, common forms of which are snagging and off-hand grinding, is done primarily to remove stock that cannot be taken off conveniently by other methods from castings, forgings, billets, and other rough pieces. The major costs of a grinding operation are those incurred for labor, time, overhead, and the abrasive wheel. What these amount to depends upon: (1) the selection of grinding wheel, (2) the equipment and its operation (including such items as wheel speed, work speed, feed, depth of cut, cutting fluid, and wheel dressing), and (3) the work piece and its material. How these factors affect costs and how they should be controlled for best results will be explained in this chapter.