This chapter introduces some background regarding the hearing system, sound and audio that may be beneficial when conducting sensory evaluation studies of sound. It reviews some basics of acoustics and audio engineering that may be helpful when implementing and testing sound technology. The chapter describes the sense of hearing, which consists of two ears and a considerable amount of dedicated neural processing in the brain. The hearing mechanism makes its best efforts to understand “what” caused a sound, and “where” the physical objects that caused the sound is located. Even more important is to understand the general working principles of hearing when studying its function in the context of complex sounds. The purpose of hearing is to capture sound arriving at the ear and analyse the content of the signal to deliver information about the acoustical surroundings to the higher levels in the brain.