It is common for audio signals to be played on stereo systems consisting of two speakers (i.e., headphones or loudspeakers). A recorded, mono signal from a single microphone is converted to a two-channel, stereo signal to be played through one or both of the speakers at the same time. Audio engineers control the perceived position across the stereo field of a recorded signal using panning. Another processing technique used to add audio effects to a stereo signal is mid/side processing. These topics are presented in the current chapter.