The Introduction of this chapter deals with origin of the yet other important cognitive control skill called Metacognition, and the reasons why it is a Fuzzy Concept is illustrated by citing the meaning and definitions clearly. The various exponents of Metacognition John Flavell, Ann brown, John Borkowski, Michael Pressley, Robert Sternberg and Tobias & Everson with their models and theories are given in this chapter to make a thorough understanding of the theoretical postulates of Metacognition. The research undertaken to prove the effect of Metacognitive skills on Problem Solving, Learning Disabled, Reading Comprehension, Second Language acquisition, Memory and Motivation are supported with empirical evidences. This crucial CCS is very important for teachers to become reflective practitioners are presented. The process of development of Metacogntion, its role in Brain, its role in academic success are all elaborately dealt with. Various metacognitive strategies are added as classroom practices to improve metacognitive abilities and skills among the learners. The assessment of this cognitive control skill among the learners is the crucial responsibility on the part of teachers.