I first published The Music Theory Cheat Sheet in 2019. I wanted to create a quick-reference music theory guide that I could use while practicing, writing, and teaching that would help me internalize the modes of the diatonic scales, and serve as a handy resource for my students to begin applying the theory we covered in lessons in their own playing. While I did learn to read music at a young age, I have rarely needed to apply that skill in my day-to-day life as a working musician. Having a sound understanding of music theory from the perspective of intervals and harmony, the Nashville Number System, and the relationship between the modes of the major scale has served me well for many years and across several different professional contexts. For that reason, you will not see sheet music or notation in this book. This edition expands on the first edition of The Music Theory Cheat Sheet by incorporating chord charts for guitar and piano, as well as a fourth section with The Circle of Fifths. It also has an accompanying interactive web application that will help you ‘hear’ the concepts in each section, with playable keyboards, fretboards, and many other interactive tools to help you apply these concepts in your own playing. In short, this tool is what I wish I had when I started, over twenty years ago. I hope it helps you.