This is a long and careful buildup of the mathematical machinery of string theory, patiently developing the tools theorists use to work this subject. The book is carefully laid out and shows the high quality materials which can be achieved when a text is developed out of a real course tested with real students over a period of time. It is an introduction to string theory which leaves no term undefined, no basic undeveloped but brings the student to the threshold of current research in a logical sequence. I find it easy to read and follow Zwiebach's style of writing.<br><br>However, this is not a 'popular' book. There are such 'popular' books which attempt to give some elements of string theory or other contemporary physics or cosmology but fail miserably. A classroom text won't have that problem. (To see an example how NOT to communicate string theory to anyone, take a look at "The Little Book of String Theory" by Steven Gubser of Princeton, which substitutes analogies about dancing for real teaching, and is of little value to readers of any background.)<br><br>No one should make the mistake the Zwiebach book is for the general reader - it is not. Don't be misled that it is an undergraduate course text; true, but an MIT advanced undergraduate text, for elite MIT physics pre-professionals who are at the level of graduate students elsewhere. Also their preparation is extensive and uniform. The book is perfectly understandable for the physics student on a PhD track and already familiar with electromagnetism, relativity and quantum mechanics. But not otherwise. For example, there is a one page review of the variational principle of least action in mechanics; no one who hasn't studied this before is going to learn it in one page. Besides the target audience of professional-track MIT students, the book may be accessible for self study by physicists and engineers working in other fields who want to understand what all the shouting is about and are willing to put in the time and concentration. The second edition corrects numerous errors and misprints of the first edition which could cause much puzzlement otherwise.<br><br>It is a lot of work to develop a polished text like this and many universities unfortunately do not really reward research faculty for doing so. MIT is different and Prof. Zwiebach has received well deserved honors for producing the course and the book. As string theory is one of the frontier intellectual explorations of humankind in our generation, it is a worthy subject to learn and to teach.