As an English teacher to foreign students for the past 8 years, I have found this book invaluable. It has an excellent index at the back which makes it child's play to find out, for example, what the difference is between "that" and "which" and when to use each one, with helpful examples. Everything is explained clearly and the book is appropriate for intermediate to advanced students to use on their own. I have bought 4 copies of this book over the years, giving two to my advanced-level students for their own use and passing one on to a teacher about to teach English for the first time. I really can't recommend this book enough - you will not be disappointed.