I bought the book to build and enhance my improv skills. I've been playing the trumpet for 20 years part-time professionally and figured that I could jump right into the book and start jamming. I was wrong. Despite being a musician for this long, I never had an understanding of chord structures, and I found out quickly that you must understand chords if you want to use this book. So, I had to buy a music theory book first and now this book is making more sense to me. I give it 5 stars for usefulness and quality, but 3 for assuming that you know chords first.