Since the publication of the first edition in 1975, the communicative approach has established itself as an efficient and popular method for teaming foreign languages. During this time, A Communicative Grammar of English has established itself as an innovative grammar and a successful text. It is now brought fully up-to-date by this second edition which is fully revised and redesigned for accessible usage.
It's more of a reference book than a book to read through, but the explanations are clear and the examples generally useful. Back in 1975, when it was first published, it was probably a godsend. The third edition incorporates some corpus data, which keeps this book relevant today.