Modern Heat Treatment should be considered as an art or trade, since it certamly requires knowledge, skill and judgment for its proper performance. These, in turn, necessitate at least some knowl edge oi heat, of steel, and of the effect of heat upon steel. And all three factors are linked together by the human element. The author has therefore endeavored to bring together the theoretical and practical sides of the general subject of steel and its heat treatment in such a manner as will, he hopes, be understandable by that human element. It has been the author's attempt to make the chapters dealing with the heating problem more of a heat talk than of a furnace talk of heat application rather than details of construction; of the importance of the human element and scientific efficiency rather than the elimination of the human element through scientific management; and finally, of viewing the heating problem as an engineering prop osition, adapting each fuel to proper furnace design and operation to meet the requirements of the problem in hand, and by so doing aim for the adoption of the standard heating unit in terms of finished product the cost of a unit of quantity of given quality.