This book is an excellent introduction to superstring theories, mostly readable by non-experts. The author has deep knowledge of the different matters that are treated in the book, and he is able to explain them in a way that can be easily understood. For me, the best is the excellent analogies that simplify the explanations of the different matters. It is very common in these types of books to use analogies, but they are usually too simple, and difficult to associate with the real thing. In this case, the author is able to find really good examples.<br><br>I think it is a very recommendable book. One thing that I did not like much was the excessive length of the explanations devoted to the author's own achievements in this area. No doubt at all they are very important, and it is good to reflect that the author has been deeply involved in the developments of the superstring theories, but I think that a lighter approach would have been better. And another weak point of this book, from my point of view, is the excessive enthusiasm for these theories, in spite of the lack support from experimental results. Apart from that, I enjoyed the book.