The purpose of this dissertation was to examine metacognition among academically talented middle and high school mathematics students from both educational psychology and mathematics education perspectives. A synthesis of the literatures and three studies employing quantitative, qualitative, and mixed methodologies were used to address three research questions: (a) What is metacognition, (b) What are the relationships between metacognition and academic achievement, and (c) How should educational psychologists measure metacognition? Literature review findings suggested four metacognition constructs: knowledge, regulation, beliefs, and awareness. Examples of students’ metacognition during mathematics problem solving with regard to each of these constructs were provided. Results of exploratory factor analysis indicated that scores on an existing metacognition questionnaire were structurally valid although they lacked concurrent and predictive validity. Metacognition as measured by the existing questionnaire was not significantly or meaningfully related to measures of academic achievement or problem solving metacognition. However, problem solving metacognition was related to both problem solving accuracy and students’ diagnostic test score and summer course grade. Findings from this study suggest that more research is needed in order to (a) create a coherent definition of metacognition that is both taxonomical and functional, (b) examine the complex relationships between metacognition and academic achievement, and (c) create a metacognition self-report questionnaire with sound psychometric properties.