The book is a reference guide in an encyclopedic format aimed to promote critical thinking of graduate and postgraduate students. It will help intended readers to cope with the similar terminologies which are often used for evaluating students' content knowledge. It was designed in a practical format with clarity and comprehensiveness to provide an easy to understand definition to get a quick picture. Reading the key concepts in applied linguistics will help the readers consolidate the problematic key terms in Education. The book will be a core adoptable text or supplementary reading. Thus, it will be useful for marketing purposes at different department such as Education, Teaching English as a Foreign /second language (TEFL/TESOL), Psychology, Social sciences, Educational administration.