The theory for the propagation of electromagnetic waves in gyrotropic media with boundaries is reviewed. Media which simultaneously exhibit a natural activity and a magneto-optic activity are discussed. The optical irreversibility effects in such media are analyzed. Magnetic crystals with a natural optical activity are discussed. The meaning of the magnetic permeability at optical frequencies is discussed. The optical properties of magnetically active ferromagnets are examined in the case of coincident roots of the dispersion relation. The propagation of light in a bigyrotropic medium is also discussed. Certain distinctive properties stemming from the existence of two types of gyrotropy, anisotropy, and absorption are discussed. The mechanisms for circular dichroism and the features of the dichroism of naturally gyrotropic media in an external magnetic field are discussed briefly.