Learning to read with understanding is the most important achievement in a young student’s life. Unfortunately, many students are unable to comprehend texts, even though they can decode them fluently. Consequently, teachers, researchers, and other educators have begun focusing on early comprehension instruction. This chapter addresses the role of metacognition in teaching reading comprehension to primary students. It includes a review of studies on the development of metacognition and a review of instruction designed to develop metacognition both in young children and in teachers. We begin with a short discussion of some of the basic concepts relevant to the study of comprehension and comprehension instruction. Variation in the way these concepts are defined sometimes leads to confusion.