I picked up this book to find out where string theory came from and it satisfied my curiosity. It's very clearly written and a lot of fun. Even if string theory turns out to be wrong, applying physics to higher dimensions is still a great review of the 4-D variety.<br><br>The author says this is a textbook for undergraduates but I don't think I would have had enough quantum mechanics to understand it until after my first year of graduate school. In addition I'd suggest readers have a background in special relativity, the Lagrangian formalism, E&amp;M, and at least an intro to quantum field theory.