This book argues that, to teach languages well, one needs to know how people learn them, and that current English Language teaching (ELT) practice largely ignores this vital question. It offers an up-to-date, accessible discussion of recent developments in knowledge about second and foreign language learning, as well as implications for language teaching. It then provides a critical analysis of the current ELT industry, arguing that its increasing commercialization has led to poor teaching, dull materials, inadequate second language teaching education, and testing procedures that are unfit for purpose. The book then moves on to expose the often-hidden political and economic interests at work, and ends with suggestions for how ELT should be organized to the benefit of learners, teachers, teacher educators and testers alike. It will appeal to undergraduates and masters students of teaching English as an L2 or applied linguistics, as well as practising teachers.