I purchased this approximately 10 years ago. There is some aging, such as sun damage, but the inside is generally clean. A few pages of the level 0 problem set have some writing by a child, which I erased with an eraser (see the last photo). I have looked through the rest, but I believe there are no other markings, although please forgive any oversight. Also, please understand that this is a used item stored at home, so please purchase only if you are comfortable with this. This is a set of 4 books.