In the real world, audio is crucial to art, entertainment, and oral communication. Audio recording and reproduction can be considered a VR experience by itself, with both a CAVE-like version (surround sound) and a headset version (wearing headphones). When combined consistently with the visual component, audio helps provide a compelling and comfortable VR experience. Each section of this chapter is the auditory (or audio) complement to one of Chapters 4 through 7. The progression again goes from physics to physiology, and then from perception to rendering. Section 11.1 explains the physics of sound in terms of waves, propagation, and frequency analysis. Section 11.2 describes the parts of the human ear and their function. This naturally leads to auditory perception, which is the subject of Section 11.3. Section 11.4 concludes by presenting auditory rendering, which can produce sounds synthetically from models or reproduce captured sounds.