An excellent update of a classic text. This book, in just this one volume, gives you an incisive description of information theory. It assumes that you have no prior experience in this field. It develops the theory from the first principles of Claude Shannon, and rapidly shows you his major results.
If you are a student, a valuable and essential part of the book are the several hundred questions. You really need to tackle as many of these as you can. By doing so, you can substantially deepen your understanding of the subject. The problem sets are probably also another reason why this book has become a common text in Information Theory classes.
The first edition of this book (and now hopefully this edition!) has been compared by some to Richard Feynman's Lectures on Physics, as a standard and authoritative book in its field.