Electrodynamical properties of magnetically ordered media are analysed theoretically. Two types of magnetic materials, namely ferromagnets and antiferromagnets, are considered and the effect of the magnetic subsystem on the properties of the host metal is discussed. Various types of elementary excitations, such as magnetic polaritons, magnetostatic waves, and magnons, are examined within the conventional quasiparticle framework. The dispersion of the quasiparticles as a function of the relation between the characteristic frequencies of electrical and magnetic nature is described over a wide range of frequencies. Particular attention is given to the statistical thermodynamics and kinetics of magnetic materials. The possibility of Bose - Einstein condensation in a magnon gas is analysed and the kinetic theory of electron-assisted magnetostatic wave damping in a ferromagnetic metal is developed. The dispersion of surface polaritons is examined in detail. Examples of solutions of spatially non-uniform problems are discussed with allowance made for spatial dispersion, which show this latter to be of particular importance in antiferromagnets.