This chapter summarizes the research work presented in this monograph on sound manipulation based on various acoustic metamaterials, including acoustic asymmetric transmission, acoustic focusing, and acoustic asymmetric focusing. Several key innovations include subwavelength phase-controlled lenses, broadband thermoacoustic devices, and multifunctional focusing systems, enabling breakthroughs in medical ultrasound, underwater communication, and nondestructive testing. In addition, the chapter emphasizes emerging research directions such as three-dimensional wavefront control, active tunability, and machine learning-assisted design. These developments establish new paradigms for next-generation acoustic technologies with transformative applications across biomedical, industrial, and environmental fields.