This book is marvellous. As a linguist, I highly commend and indeed recommend this book. The reviews above certainly don't do it justice, but then this one doesn't either. It's not a rambly "this is how English was synthesised" book like "The Adventure of English", at all. It's more of a textbook. It aims to give the reader the key to learning all Romance languages as a one-er, using their similarities and differences as a useful tool for learning rather than a hinderence. It does the same with Teutonic languages, and how they all do the same, in their own way. From this 669pp book, one can easily learn the core matter of French, Spanish, Italian, Portuguese (on the Romance side of things) and German, Dutch, Danish, and Swedish (on the Teutonic). However, it also gives excellent insights into languages as varied as Latin, Greek, Gothic, Anglo-Saxon, Icelandic, Esperanto, etc. It covers the web of vocabulary, the web of grammar, and all that holds the dynamic world of languages together.
I have many many language / linguistic textbooks, this is by far my most prized one. Well, no, it's my favourite one. Not my most prized, because it's freely available to re-purchase, should anything happen to my copy. My most prized ones are old, yellowed, out of print, and irreplaceable ;) But this is the _best_ book. A must have for any linguist, whether professional / student / lay interest.