Musical Instrument Digital Interface, or MIDI, is the standard way in which we interact with music in the digital world. Think if it as the DNA of your musical performance. Without it, our ability to compose, produce and perform music in modern times would be remarkably different. In this chapter, we will have a look at what types of messages MIDI contains, that is, how it allows humans to communicate with computers and digital instruments in a universal binary language. Using what we know about MIDI, we will then apply this concept to the Pro Tools environment, and most importantly, we’ll start making music!