It is the experience of most language teachers that the single, biggest component of any language course is vocabulary. No matter how well the student learns grammar, no matter how successfully the sounds of L2 are mastered, without words to express a wide range of meanings, communication in an L2 just cannot happen in any meaningful way. And yet vocabulary often seems to be the least systematized and the least well catered for of all the aspects of learning a foreign language. The purpose of this book is to look at what we do know about the vocabulary of a language like English and to reflect on how this has been applied in language teaching.