<p>With the rapid advancement of the Internet of Things (IoT) and the widespread use of smart devices, acoustic sensing technologies and applications have experienced notable development during the past decade. We survey the state-of-the-art acoustic sensing systems to understand the principles of acoustic sensing technologies better and explore future trends. Particularly, beginning with acoustic signals’ physical properties and sensing mechanisms, the survey gives a comprehensible review of core techniques, typical applications, and their performance outcomes. Firstly, the survey derives the core principles by analyzing the key components of acoustic sensing systems, based on which we group existing sensing technologies into two categories, i.e., channel state estimation and target state estimation. Then, according to the granularity of target activities, the survey divides acoustic sensing enabled applications into three categories, which are fine-grained signal detection, medium-grained motion sensing, and coarse-grained activity recognition. Accordingly, we find that different sensing techniques have distinct advantages and limitations across varied applications. Last but not the least, by discussing the challenges and open issues, the survey highlights several research opportunities for the next generation of acoustic sensing.</p>