In this essay, I investigate musical silence. I first discuss how to integrate the concept of silence into a general theory or definition of music. I then consider the possibility of an entirely silent musical piece. I begin with John Cage’s 4′33″, since it is the most notorious candidate for a silent piece of music, even though it is not, in fact, silent. I conclude that it is not music either, but I argue that it is a piece of non-musical sound art, rather than simply a piece of theatre, as Stephen Davies has argued. I end with consideration of several other candidates for entirely silent pieces, concluding that two of these are in fact pieces of music consisting entirely of silence.