This chapter discusses the affective domain of self-regulation, also described as autonomy supporting, self-initiation, self-activation, self-generating, self-organizing, self-directed, self-discipline, self-monitoring, self-evaluation, responsible decision-making, co-regulation, relationship management, time planning and self-management, socially-shared regulation, and the metacognition involved in writing and developing as a writer. There is a large amount of empirical evidence now available showing the positive link between self-regulated metacognitive learning and academic achievement. Theory, research, and educational practices associated with developing children’s self-regulation in writing and its important role in developing confident and effective writers are explored. This includes discussing the typical behaviours witnessed in a rich variety of educational research and differences observed in the behaviour of pupil-writers with high and low levels of self-regulation. Finally, the authors describe the relationship between developing apprentice writers’ self-regulation and the 14 principles of effective writing teaching. They give examples of the kinds of instructional practice carried out by the most effective teachers of writing.