This is an excellent book. Having recently read two other books about astronomy which I had found totally incomprehensible, this was a great find. It is brilliant, engaging and accessible.
The book looks at the basic idea of string theory which is that everything in the universe is made up of vibrating strings and then looks at the implications of this, including multidimensional universes and discussing whether string theory could be the grand unifying theory of everything.
Those who are serious physicists, mathematicians or astronomers may find the occasional light hearted and surreal explanations of things sometimes a little frivolous. However, I'm a biologist, who during my degree, took an extra class in astronomy and walked out after two weeks of incomprehensible lectures, though I've always been interested in the topic. For me, the use here of George and Gracie the characters who float through space in illustration of relativity and then become physics professors in a 2 dimensional universe in illustration of multi-dimensional space was a touch of sheer genius. Not that I really feel that I understand string theory even now (I did lose the thread a little in the last third of the book and there's a lot of science and maths, especially in the 400 pages of the book!) but this is a great book for those with some grasp of scientific thought who are interested in finding out more about this topic.
The Elegant Universe by Brian Greene, published by Vintage