This easy to read and relatively small book attempts to cover body language in a variety of areas of human interaction, and therefore barely scratches the surface in interpreting body language. You may not be able to read a person like a book just by reading this book, but this book is a decent introduction into body language.
The authors appropriately point out that different gestures and expressions in isolations are just like words, and that it is important to take into consideration how these different gestures and expressions relate to each other, how much they support the meaning of each other, the verbal language that accompanies them, the individual's cultural background, the health condition of the person, individual's habitual behavior, possible environmental factors, and anything else that may be contributing to the expression of a particular gesture.
At the beginning of the book, some expressions, gestures, postures and body movement are illustrated. Later chapter of the book, in an attempt to cover as many different situations for observing the body language as possible, there is only a listing of expressions, gestures or postures to which you may want to pay attention.
People who work in occupation where their well-being and/or income depend on their skill to interpret the body language they deal with (such as salesman, negotiators, lawyers, flight-attendants, waitresses, therapists, presenters, etc), will most likely know much more than they could find in this book. And when it comes to body language related to courtship and relationships, there are other books that offer much more information, like The Flirting Bible.
This book does share a few pages on body language children may use to communicate, body language in courting, body language used in negotiations, body language used in sales, body language used in a courtroom, body language used at social gatherings, and you may find it useful as a general overview and a brief introduction, and then keep up exploring other books, perhaps What Every Body is Saying, The Definitive Book of Body Language, Winning Body Language, The Naked Brain, and whatever else piques your interest.