This book is intended for researchers, engineers, and students who have an interest in designing acoustic sensing solutions on commodity devices. The authors provide an in-depth coverage of the basic building blocks, state-of-the-art algorithms for active acoustic sensing on commodity devices, design considerations, and novel applications they enable. The authors start by providing a comprehensive overview of diverse active acoustic sensing applications. They then discuss the fundamental acoustic signal processing and acoustic waveform design techniques. Finally, they delve deeply into three specific categories of acoustic sensing applications: aerial acoustic communication, spatial context awareness, and physiological and behavior sensing. Each category of applications is thoroughly examined, covering aspects such as motivation, problem setup, existing solutions, case studies, and open problems. Additionally, the authors provide reference implementations of key algorithms discussed in the book.