As an equivalent counterpart of topological research on photonics and condensed matter physics, acoustic metamaterials create an opportunity to explore the topological behaviors in phononics and physics of programmable acoustics. This book introduces the topological behavior of acoustics through the novel design of metamaterials. It provides valuable insight into acoustic metamaterials, from multidisciplinary fundamentals to cutting-edge research. The word ‘meta’ is now more popular than ever due to social media activities. ‘Meta’ is a word originated from Greek which means ‘beyond’. Thus, a metamaterial is the material that by definition does not exist in the world and its features are beyond the capability of current materials. A metamaterial is artificially made material by researchers. While comprising various internal components and exploring various geometric patterns, counter-intuitive physics or phenomena were explored by the researchers in metamaterials. Generally speaking, metamaterials developed in acoustics are periodic in nature. Periodic acoustic media can be one dimensional (1D), two dimensional (2D), or three dimensional (3D) in nature.