A typical performance situation of a vocal ensemble or choir consists of a group of singers in a room with listeners. The choir singers on stage interact while they sing, since they also hear the sound of the neighboring singer and react accordingly. From a physical point of view, the choir singers can be regarded as sound sources. The properties of the room influence the sound and the listeners perceive the sound event as a sound receiver. Furthermore, the processes in the choir can also be described acoustically, which affects the overall performance. The room influences the timbre of the sound on their way to the audience, the receiver. Reflection, absorption, diffraction, or refraction influence the timbre in the room. The sound in a performance space can be distinguished between a near field very close to the singer and a far field. The distance at which the far field can be assumed is strongly dependent on the acoustics of the room. Especially for singers within a choir, the differentiation between those sound fields is important for hearing oneself and the other singers. The position of the singers, their directivity, and the seating position of the listener in the audience will have an influence on listener perception. Furthermore, this chapter gives background information on intonation and synchronization aspects, which are most relevant for any vocal ensemble situation. Using this knowledge, intuitive behavior and performance practice can be explained and new adaptations can be suggested for singing in vocal ensembles.