This dissertation research is a theoretical study of magneto-optic properties of magnetic transition metals and metallic compounds based upon density functional theory and electronic structure calculations. The origin of magneto-optic effects is discussed. A derivation of a practical implementation of the Kubo formula is presented. The complex polar Kerr rotation spectra of Fe, Co and Ni, the NiAs structure compounds MnBi, MnSb and Mn2BiSb, as well as several L21 and Clb Heusler alloys are investigated with LMTO and FLASTO calculations. In general, when compared with experiments, these band structure calculations within the local spin density approximation (LSDA) yield satisfactory results. The large Kerr rotation in PtMnSb is found not to be a result of its half-metallic characteristics. The limitations of LSDA and linear methods are also discussed