As discussed in Chap. 2 , if music embodies the “creative order of all things in the cosmos,” considering the nature of the sounds that constitute music is essential. This chapter explores sounds from a relatively modern perspective. What is sound? We live surrounded by sounds. Those sounds may be music, mere sounds, or noise. For instance, we intentionally choose to listen to music by attending a concert by our favorite artist or purchasing their albums and digital recordings. Occasionally, we hear sounds regardless of our intention to do so, including sounds of nature, such as the sound of the rain, flowing stream, or the rustling of leaves in the wind. Occasionally, we are forced to hear continuous unwanted sounds, such as the honking of cars or the whirl of the washing machine. The question is, how are such sounds produced, and how can they be defined?