I have a copy of Practical English Usage on my desk at school. I have other grammar reference books, such as Quirk and Greenbaum, at home, but this is by far the most useful for a teacher of English as a foreign language. Swan's style is to focus on the problem points of learners, and explain them and in simple, pithy and purposeful, everyday language to the extent that an advanced learner would be able to understand. As a teacher, you can often save yourself a lot of hassle simply by quoting from it. I like Practical English Usage because the examples are real, living English taken from the British National Corpus, or are realistic enough to be acceptable as such. Too many grammar books borrow their English from the past, or from the dialects of ivory-tower academics. This book redresses this imbalance. If you are not British, fear not, as another feature is its thorough coverage of the differences between British and American usage. (Other dialects are not covered.) If you are a teacher of English as a foreign language, or a smart student, you will not be disappointed with this Practical English Usage.