The chapter provides in-depth discussions about the physics, device architectures, and modes of operation, providing a comprehensive understanding of how the MEMS/NEMS-based acoustic devices work. The chapter explains the fundamental concepts of acoustic and then discusses the design and operation of various acoustic devices, such as surface acoustic wave (SAW) devices, bulk acoustic wave (BAW) devices, film bulk acoustic resonators (FBARs), and photoacoustic devices. The chapter emphasizes the importance of materials and manufacturing procedures for device performance and provides insights into acoustic device material choices. Moving on, the chapter expands into the relevance of acoustic devices in gas sensing applications, illustrating how these devices use their unique features to detect gases precisely and quickly in a variety of situations. Furthermore, the chapter explains how acoustic devices play an important part in 5G/6G communication systems, where they act as oscillators and filters to improve signal processing, filtering, and frequency management.