This book is summarizing the state of the art of metamaterials from the point of view of rational and applied mechanics. It contains 15 chapters written by well-known researchers in the field of acoustics and mechanics of metamaterials and includes in-depth discussions on mechanical and acoustical properties of metamaterials, covers a vast array of methods enabling to elaborate models of metamaterials and research their properties, provides a forecast for the development of metamaterials and their applications.