This chapter shows that the electric susceptibility tensors for crystals of all 32 crystal classes are derived for arbitrary orientations of the magnetization vector under the assumption that the effect of magnetic ordering on the tensor elements is small. It considers the effect of cubic and orthorhombic symmetry on the proper values of energy and corresponding proper states for s-, p-, and d-states and compute the susceptibility tensor spectra for simple situations. The symmetry operations of a particular crystal point group leave the material tensors unchanged. The crystal rotation about an axis in the space affects the form of the electric susceptibility tensor. The Lorentz model represents the simplest microscopic approach to the medium response to an electromagnetic plane wave. The particle moves under the action of the Lorentz force produced by a homogeneous time-constant magnetic field and electric and magnetic fields varying in space and time, which constitute an electromagnetic plane wave.