The purpose of this chapter is to cut through the fuzziness surrounding the concept by describing the characteristics of metacognition that have remained relatively constant across disciplines and purposes since John Flavell’s pioneering work helped give form to the concept and whose call for research provided an impetus for its study. In addition, greater under­ standing of metacognition can be gained by knowing how it has been investigated. Therefore, a brief review is given of the ways in which meta­ cognition has been operationalized and investigated. By attempting a defi­ nition of metacognition and describing how researchers have come to know the concept, some of the fuzziness should be resolved.