To correctly diagnose a human organism with the help of acoustic waves is impossible without knowledge of the physics of acoustic waves interaction with the issues of the organism. This book is dedicated to the given problem. It consists of four sections, the first of which deals with physical models of the biological issues used in ultrasonic diagnostics. In the other sections the basic stages of ultrasonic diagnostics (sound radiation, sound scattering, depictions visualization) are studied. It is shown how different bodies and issues of a human organism scatter acoustic waves and how, using the scattered wave, one learns about what happens with some body or issue.