Our goal is to discuss how the research on metacognition in mathematics can be interpreted from the perspective of constructivist theory. Much of what we present in this chapter is speculative in that very little theory or research has examined conscious reflection from a constructivist perspec tive. First, we discuss issues central to the development of metacognition and its relationship to problem solving. We then discuss the extant literature on metacognition in mathematics, specifically focusing on strategy knowl edge and metacognitive awareness. We end with a discussion about how metacognition may be conceptualized from the perspective of radical con structivism and social constructivism, and focus on the potential implica tions of constructivist theory for the instruction of metacognition in mathematics.