Theatre almost always involves sound-making of some sort, from the stage and from the audience, and even in the absence of designed, intentional sound the ambient environment may still produce something to hear. This chapter introduces some key topics in the academic study of theatre sound, referring to a variety of scholarly texts in this area of specialisation. Topics addressed include the scripting of sound and silence in dramatic texts; designed and circumstantial elements of theatre sound; the acoustical design of theatre buildings; voice and speech; audiences’ aural experiences; and soundscapes of the theatrical past. This conceptual overview is supplemented by a short analysis of a recent example of sonically inventive theatre by Complicite/Simon McBurney called The Encounter, in which audience members use headphones to listen to a performance that prominently features recorded, binaural sound and live-sound making. This case study, which resonates with many elements of theatre sound studies discussed in this chapter, demonstrates how sonic analysis of contemporary theatre may be conducted and what can be learned from this type of analysis.