Chomsky's approach to linguistic description became widely known as a result of the publication of "Syntactic Structures" in 1957. In the following decade, transformation-generative grammar - "TG" for short - has established itself as one of the most vigorous and exciting movements in modern linguistics, and one which many people believe has far-reaching implications for the study of human cognitive processes. The aim of this book is to present the main outlines of transformational theory, using as far as possible Chomsky's own words, but arranged in such a way that a non-specialist will have no difficulty in following the text. The topics covered include syntax, phonology, semantics and language acquisition. In the final section, some of the implications of transformational theory for language teaching are considered.