A book about languages, how to learn them and how they are related. The author has an extensive knowledge of germanic languages (english, german, danish, dutch, swedish, norwegian) and the latin family (latin, french, italian, spanish, portuguese) and explains you how they are related and how the learner can take advantage of it. If only we had more books that still dare to explain complex things in simple words !

As an example of the style of the book, here's a paragraph where he explains the reason why people have such a hard time learning languages in schools, namely, why "generally, the adult has more to show after a three month's course at a commercial institute than an adolescent after three years' study of a foreign language in a British Secondary or American high school" :

"The greatest impediment, common to most branches of school and university education, is the dead hand of Plato. We have not yet got away from education designed for the sons of gentlemen. Educational Platonism sacrifices realizable proficiency by encouraging the pursuit of unattainable perfection. The child of the immigrant learns a language by blundering his or her way into greater self-confidence

You can get it from Amazon.com for about 12$, which is the best price I found.