The fifth volume of the collected works of Professor M.A.K. Halliday, The Language of Science explores the semantic character of scientific discourse. The chapters are organized into two sections, one being on grammatical metaphor; the other dealing with scientific English. In language, there exists the potential for constructing new discourses, among them scientific discourse. The volume opens with a new work from Professor Halliday addressing the question, How big is a language? It is a question that goes to the heart of the paradigmatic complexity, or meaning potential, that characterizes language.