The book is based on the lectures, given by the authors at the Physics Department of the Lomonosov Moscow State University (Neutronography chair). A brief description of the theoretical methods, based on the two-time correlation functions and their extensions, is given. These methods are further applied to study the basic models of theory of the collective excitations in crystals and simple liquids. The actual topics of the physics of soft matter, where theoretical methods of the physics of condensed state play a major role, are considered.