Researchers increasingly point to the importance of metacognition in enhancing language learning and teaching. The aim of the first part of the chapter is to clarify the concept of metacognition and discuss how metacognition relates to language learning and teaching. In the second part, common methodological tools and approaches to metacognition research, including examples from the field of language learning and teaching, are presented. Thereafter, the focus is on how learners' metacognition can be promoted, and the aspects of language teaching that teachers should be able to reflect on in order to enhance their own and their learners' metacognition. The final section discusses the extent to which language teachers have actually implemented a metacognitive instructional approach to language learning.