All of these books titled "Problems and Solutions on (subject): Major American Universities Ph.D. Qualifying Questions and Solutions" are invaluable tools for a physics graduate student, in my experience. When doing homework assignments, studying for exams or the qualifying exam itself, most graduate students should be elated to have an arsenal of solved problems at their disposal. I have purchased nearly every one of these books and I use them often. The biggest books (mechanics, quantum, and E&M) are fantastic resources for qualifier problems and examples. When I show these books to my fellow students, they immediately ask me where they can get a copy of their own.One criticism: The index is sparse. It seems as though many problems are not listed under obvious key words. However, I have a suggestion for those that are also frustrated by this. Whenever I encounter an interesting problem, I go into the index and look under all of the obvious key words. If the problem is not listed, I add the problem number to the index in that spot. In all of my copies of these books, I am creating a comprehensive index. It takes time, but it is almost instructive to do this editing for it makes one more familiar with the book.One other thing: I haven't found many errors, but I have found a few. Usually they are not apparent until one is working through the little details of a problem.If you are a student in physics, I suggest that you get your hands on these books.