The paper has been written on the subject of magnetic sheet materials for electrical plant, and the nickel-iron and similar alloys used in light-current work are not specifically dealt with. The paper represents an attempt to stimulate the interest of electrical engineers and others in this class of sheet steels, in which progress in relation to the commercial materials has been relatively slow.After a short discussion of the historical development, the limitations imposed upon designers of electrical plant by the existing materials are referred to. This is followed by a brief outline of the physical basis of magnetic processes and by a discussion of the factors which affect the magnetic properties of electrical sheets. Finally, reference is made to future possibilities.