In this paper, theoretical methods are presented for calculating the depolarization of ice clouds. Rayleigh scattering from single particles is used. A general theory is introduced that includes distributions of ice particle shapes and orientation angles for both single and multiple scattering. It is shown that the more accurate multiple scattering formulation yields cross-polar discrimination values significantly worse than those for single scattering over the 10- to 30-GHz band for high ice content. Comparisons are made to measurements using the SIRIO satellite.