Indoor acoustic positioning systems operate by transmitting and receiving sound signals to estimate the position of objects or mobile platforms within enclosed environments. In contrast to outdoor scenarios where satellite-based technologies such as GPS are highly effective, indoor environments present a range of challenges, including signal blockage, multipath propagation, and acoustic reflections. These complexities require alternative positioning solutions that rely on sound, particularly in situations where electromagnetic interference must be avoided or where high spatial resolution is necessary with minimal infrastructure. This chapter introduces the foundational concepts of acoustic positioning, beginning with a discussion of how sound propagates in indoor environments. It then outlines key measurement techniques that utilize time, angle, and amplitude information to determine position. Understanding these physical and algorithmic principles is essential for the development of accurate and reliable indoor localization systems, applicable in a variety of scenarios such as industrial buildings, greenhouses, and autonomous robotic navigation.