This book briefly introduces the main approaches, theories, hypotheses, and models in the field of second language acquisition outlining key terminologies in each as well as their basic claims. The book provides the intended readerships with a substantive source by which they can acquire an immediate experience with ins and outs of the trends in second language acquisition. It offers students introductions to the core topics in encyclopedia-like descriptions of various concepts used in the L2 professional literature. The most outstanding feature of the book is its clear and concise description of the content knowledge and controversial topics dominating polemical debates defining the interlocking dimensions comprising the field of English language teaching. Citations provided at the end of each concept will lead the reader to original. The sketchy overview of the main issues, terms, and people introduced makes the book a must-have reference for MA students, PhD students, teachers and researchers in applied linguistics.