First off, the content of this book is top-notch. Calculus of Variations comes across as slightly magical when you first encounter it, but this book lucidly explains in thorough detail how and why you can extend calculus to functions of functions.That said, the binding of this book is really terrible. The cover--which is glued on--fell off after I opened the book 4 times! That is unacceptable, even for a book as inexpensive as this. The printing quality also isn't great, and some glyphs are difficult to discern, but it's not a huge deal compared to the cover falling off. Usually Dover books are better than that.