This document is the introduction to the 4th edition of the Turbocharge Your GMAT Sentence Correction Study Guide published in 2012. It provides an overview of the guide's contents which include a GMAT idiom list, common grammar errors to avoid, detailed explanations of tested grammar topics, tips and strategies, a grammar review covering parts of speech and concepts, and 250 practice questions. It also includes brief descriptions of other books and materials in the Turbocharge Your GMAT series and information about Manhattan Review, the publisher, and its founder.