The book is an introduction to the theory of elastic waves. It sets out the general laws of the behavior of elastic waves in various acoustic situations, establishes points of view that allow uniform consideration of heterogeneous acoustic phenomena, and elucidates the internal relationships between phenomena. The main attention is paid to a detailed clarification of the physical essence of the issues being dealt with, without involving a complex mathematical apparatus. The book includes a number of questions presented so far only in special scientific literature. The main content of the book refers to the study of flat and spherical elastic waves of different types, as the main types of waves found in most theoretical and applied problems. A large number of detailed tasks also allow you to use the book as a reference. The book is based on the course of general acoustics, read by the author at the Moscow Institute of Physics and Technology.