The book is devoted to the study of vibrations of dynamic systems consisting of various subsystems and having a hierarchical structure, as well as to the identification of the main patterns in the oscillations of such systems. The problem of isolation in a large system of a relatively small number of elements that determine its dynamic properties is solved. Analytical criteria of dynamic interactions between subsystems are given, which reflect energy exchange between them. Various methods have been developed for decomposing simulation models depending on the nature of system interactions.