AbstractA general theory of reflectivity by a perfect X‐ray multilayer mirror based on the usage of a recurrent relation is developed. The reflectivity is described by the well‐known Fresnel formulae which take into account jumps of susceptibility at the boundary between the layers. The analytical solution in the frame of the most general dynamical approach is found and the condition of application of the kinematical approximation is discussed. Special attention is paid to the periodic multilayer structure containing two layers of different materials with more than one pair of these layers in the per