Based on original research and novel concepts, this book investigates the nature and use of terminology from linguistic and applied viewpoints. Throughout, problems with terminology, such as overuse by teachers and cases of synonymy and polysemy, are considered and solutions are offered. Part One looks firstly at some basic concepts, then draws important distinctions between pedagogic and scientific terminology, and between transparent, opaque and iconic terms, before examining the historical, lexical and grammatical nature of terms. Part Two attempts to estimate the value and relevance of terminology in language teaching and describes the use and knowledge of terminology in various language-teaching-related constituencies: learners, teachers, textbooks, grammars and research. It concludes with a discussion of the criteria for evaluating terms and an analysis of terms used in ELT.