There was a time when good writing would be defined simply by adverting to a few literary classics. That kind of strategy is less helpful these days, when so many different styles and voices clamor for attention. What Is Good Writing? sets the terms for a contemporary debate on writing achievement by drawing on empirical research in linguistics and the other cognitive sciences that shed light on the development of fluency in language generally. The utility of defining good writing as fluent writing in this sense -- on a par with the typical fluency in speech attained by normal adults - is demonstrated by the progress it permits in evaluating the success of current writing programs in school and university, which for the most part have proved unable to deliver writing assessments that are both valid and reliable. What Is Good Writing? indicates an alternative approach that rests on a more scientific footing and shows why reading is key and why standard composition programs are so often seen to fail.