Metacognition is a structure that is referred as fuzzy by many scholars and has very diverse meanings. Much research has been conducted for more than 30 years in order to access the inner side of this structure, which is really hard to grasp. In this paper, the review of literature aims to reveal the theoretical and educational structure of the concept of metacognition chiefly on the basis of the relevant research. Then, an attempt will be made to determine the difference between cognition and metacognition. Finally, difficulties that are encountered in the measurement of metacognition and the methods and tools that will be used in the measurement of metacognition will be determined.