Selections from Leonardo's notebooks, plus commentary, plus numerous illustrations. Not a deep dive into artistic technique, but it is interesting, and the illustrations are generally well coordinated with the text.

It's short, and written for the general public, as opposed to art historians or serious art students, so if you want more detail, more illustrations, and more depth read the recent Leonardo biography by Walter Isaacson, or perhaps one of the many art history books designed for a more specialized audience. ( )