This monograph is devoted to the systematic presentation of the theory of sound- wave propagation in layered structures. These structures can be man-made, such as ultrasonic filters, lenses, surface-wave delay lines, or natural media, such as the ocean and the atmosphere, with their marked horizontal stratification. A related problem is the propagation of elastic (seismic) waves in the earth's crust These topics have been treated rather completely in the book by L. M. Brek- hovskikh, Waves in Layered Media, the English version of the second edition of which was published by Academic Press in...