Sound plays a very important role in everyday life as well as in XR applications, as it will be explained in this chapter. Recent advances and challenges in immersive audio research are presented, discussing how, why, and to which extent there is potential for further development of these technologies applied to XR. The fundamentals of immersive audio rendering for XR are introduced before presenting the main technological challenges still open in the area. Finally, a series of future applications is presented, which the authors envision being examples of the potential of immersive audio in XR, and a research roadmap is outlined.