This article outlines a theory of the development of writing expertise illustrated by a review of relevant research. An argument is made for two necessary (although not sufficient) components in the development of writing expertise: fluent language generation processes and extensive knowledge relevant to writing. Fluent language processes enable the developing writer (especially the young developing writer) to begin to manage the constraints imposed by working memory, whereas extensive knowledge allows the writer to move beyond the constraints of short-term working memory and take advantage of long-term memory resources by relying instead on long-term working memory.