Abstract: Spin angular momentum in wave systems is a fundamental physical quantity that characterizes the polarization properties of vector fields, and is closely related to wave propagation, energy transport, and wave-matter interactions. Acoustic systems, as typical longitudinal-wave systems, have long been considered to lack intrinsic spin degrees of freedom. In recent years, however, the existence of acoustic spin has been revealed from the polarization properties of the acoustic velocity field, which expands our understanding of sound-wave dynamics and introduces a new degree of freedom for acoustic wave manipulation. This article reviews various recent advances in the emerging field of acoustic spin angular momentum. We first elucidate the origin and physical nature of acoustic spin from the perspective of the acoustic Dirac-like equation, then introduce several key angular-momentum-related phenomena, including spin-momentum locking, and discuss their potential applications in directional acoustic transport. Furthermore, the development of acoustic spin research from“local”to “global” regimes is reviewed, together with the discovery of global acoustic spin-orbit coupling. Finally, we discuss prospective applications of acoustic spin in important areas such as high-capacity acoustic information transmission, directional acoustic sensing, and integrated phononic devices.