The subject of acoustic waves might easily be considered a mature one, quite specialized, with narrow and circumscribed fields of interest and of application. The present book is an evidence of the opposite: it witnesses how the concept of acoustic wave, a collective displacement of matter which perturbs an equilibrium configuration, is a pervasive concept, which emerges in very different fields. This type of phenomena can be analyzed from different points of view, it can be exploited in different ways, and is the object of active investigations. The present book, far from pretending to give an exhaustive overview of the subject, offers instead a sampling of various points.
