The book is intended mainly for intermediate students (that is, students who have already studied the basic structures of English). It concentrates on those structures which intermediate students want to use but which often cause difficulty. The book will probably be most useful at middle- and upper-intermediate levels (where all or nearly all of the material will be relevant), and can serve both as a basis for review and as a means of practicing new material. The book will also be useful for more advanced students who still make a lot of grammatical mistakes and who need a book for reference and practice. The book is not intended to be used by beginning-level students.