I don't want to discourage anyone but if you don't know what the meaning of "music theory" is, wait until you do before you buy this book. That said, Mr. Lagrimas is a multi instrumentalist and ukulele master who has managed to put the fundamentals of jazz ukulele into print. I am less than 1/3rd through this book and I know that I will not only be a better player but will have a much better understanding of jazz and music in general because of it. I have a good collection of ukulele workbooks and this one rates at the very top. If you like Jazz and you have a ukulele, you should have this book.