The observed anisotropy of oriented polycrystalline silicon-iron sheet is discussed with reference to the results of crystal physics. It is shown that whilst the material can be regarded as homogeneous, e.g. for elasticity or magnetic torque, good agreement is obtained between theory and experimental results on the oriented sheet. An equivalent model aggregate is described which simulates very closely the observed properties of the sheet.The application of the domain theory of ferromagnetism to the anisotropy of magnetic properties is discussed, and it is suggested that the problems arising might be explained by considering the actual domain configuration of the material. Experimental results on hysteresis loss, permeability, magnetostriction, etc., for oriented sheet are considered in relation to the domain changes taking place during magnetization.The more complex phenomena occurring during alternating-current magnetization are considered in relation to the simpler magnetic properties discussed earlier.