Academic texts present subject-specific ideas within a subject-independent framework. This book accounts for the presence of academic words in academic writing by exploring recurring patterns of function in texts representing different subject areas. The book presents a framework which describes academic word use at the ideational, textual and interpersonal levels. Functional categories are presented and illustrated which explain the role of academic words alongside general purpose and technical terms. The author examines biomedical research articles, and journal articles from arts, commerce and law. A comparable analysis focuses on university textbook chapters. Case studies investigate patterns of functionality within the main sections of research articles, compare word use in academic and non-academic texts reporting on the same research, and explore the carrier word function of academic vocabulary. The study concludes by looking at historical and contemporary processes which have shaped the presence of academic vocabulary in the English lexicon.