With just under 1100 pages, this is no light-weight book, and the content matches. Penrose is an extremely capable mathematician with deep physical understanding, and it shows. It is not, however, suitable for readers with little mathematical or physical understanding. It is not a book for basic learning, but rather it seems directed at a very limited audience with sufficient background knowledge and for them it will take them far further. The book is designed to take people with advanced physical and mathematical knowledge up to Penrose's level of understanding. The first third of the book is effectively an introduction to advanced mathematics, and is interesting for this in its own right.<br><br>The book nominally takes the reader with no background information and fills this in, but I do not believe that is plausible. For example, consider the introduction to Maxwell's equations. These are introduced in Minkowski coordinates and expressed into a spacetime 2-form F, called the Minkowski field tensor, and a further space-time vector, with components expressed in matrix form that permit various symmetries to be perceived. I do not believe that anyone who had not at least vaguely become aware of this sort of approach would make much headway, but what follows is certainly elegant.<br><br>My biggest "grumble" with this book is the title: I believe "The" should be replaced with "A". The ancient Greeks founded two approaches to physics. Penrose adopts the Platonic approach, which considers mathematical forms, symmetries, and even beauty, and tries to fit reality to mathematical form. Thus towards the end, Penrose devotes a chapter to twistor theory, and in the end has to acknowledge that this is mathematically attractive, but it is difficult to take it anywhere in physics. The alternative approach, the Aristotelian approach, asks questions of nature and tries to find restrictions that lead to the correct theory. I should mention the caveat that I fall into the latter school, and with that warning, I believe that a true route to reality will involve many people working from both approaches.<br><br>Irrespective of certain reservations, I believe that anybody with some mathematical ability will gain some insights from this book (the more the ability, the more insights), and anybody interested in theory should at the very least read chapter 34, which gives Penrose's opinions on where the road will go, and the fashions encountered on it. This is a truly great piece of intellectual effort.<br><br>Ian J Miller, author of Elements of Theory