The article "Acoustic Metamaterials: From Local Resonances to Broad Horizons" by Guancong Ma and Ping Sheng provides a comprehensive overview of the development and applications of acoustic metamaterials over the past 15 years. Initially driven by academic curiosity, acoustic metamaterials have evolved into a field with diverse applications due to their unique wave manipulation capabilities. The review traces the evolution from the initial findings of mass density and bulk modulus frequency dispersions in locally resonant structures to the more recent developments in compact phase manipulation, superabsorption, and actively controllable metamaterials. It also explores new directions such as acoustic wave transport in moving fluids, elastic, and mechanical metamaterials, as well as graphene-inspired and non-Hermitian Hamiltonian structures. The introduction highlights the historical context of acoustic and electromagnetic wave studies, emphasizing the role of photonic and phononic crystals in realizing wave manipulation functionalities beyond natural limits. The concept of "metamaterials" is broadened to include subwavelength structures with novel functionalities. The article discusses the dynamics of spring-mass systems, leading to the concept of dynamic effective mass, and the realization of anomalous effective mass density and bulk modulus through local resonances. Key sections include the detailed exploration of membrane-type acoustic metamaterials, such as decorated membrane resonators (DMRs), which exhibit both mass and bulk modulus frequency dispersions. The article also delves into the principles of super-resolution and focusing beyond the diffraction limit using local resonances, and the realization of acoustic superlenses and hyperlenses. These devices enable subdiffraction imaging and wave manipulation with unprecedented precision. Finally, the article discusses transformation acoustics, which allows for the design of materials that can manipulate waves in almost any desired way by changing the coordinate system. This includes the concept of acoustic cloaking, where objects can be made to appear invisible to acoustic waves, and zero-index media, which can guide waves without scattering.The article "Acoustic Metamaterials: From Local Resonances to Broad Horizons" by Guancong Ma and Ping Sheng provides a comprehensive overview of the development and applications of acoustic metamaterials over the past 15 years. Initially driven by academic curiosity, acoustic metamaterials have evolved into a field with diverse applications due to their unique wave manipulation capabilities. The review traces the evolution from the initial findings of mass density and bulk modulus frequency dispersions in locally resonant structures to the more recent developments in compact phase manipulation, superabsorption, and actively controllable metamaterials. It also explores new directions such as acoustic wave transport in moving fluids, elastic, and mechanical metamaterials, as well as graphene-inspired and non-Hermitian Hamiltonian structures. The introduction highlights the historical context of acoustic and electromagnetic wave studies, emphasizing the role of photonic and phononic crystals in realizing wave manipulation functionalities beyond natural limits. The concept of "metamaterials" is broadened to include subwavelength structures with novel functionalities. The article discusses the dynamics of spring-mass systems, leading to the concept of dynamic effective mass, and the realization of anomalous effective mass density and bulk modulus through local resonances. Key sections include the detailed exploration of membrane-type acoustic metamaterials, such as decorated membrane resonators (DMRs), which exhibit both mass and bulk modulus frequency dispersions. The article also delves into the principles of super-resolution and focusing beyond the diffraction limit using local resonances, and the realization of acoustic superlenses and hyperlenses. These devices enable subdiffraction imaging and wave manipulation with unprecedented precision. Finally, the article discusses transformation acoustics, which allows for the design of materials that can manipulate waves in almost any desired way by changing the coordinate system. This includes the concept of acoustic cloaking, where objects can be made to appear invisible to acoustic waves, and zero-index media, which can guide waves without scattering.