Sound is something most people take for granted. Our environment is full of noises, which we have been exposed to from before birth. What is sound, how does it propagate, and how can it be quantified? The purpose of this chapter is to introduce the reader to the basic elements of sound, the way it propagates, and related topics. This will help us to understand both the nature of sound, and its behaviour in a variety of acoustic contexts and allow us to understand both the operation of musical instruments and the interaction of sound with our hearing.