This chapter deals with grammar in the narrower sense; that is to say, it refers not to all linguistic systems, but speciﬁcally to syntax and morphology. Narrow or not, this is a vast subject, relevant to very many topics which come under the heading of ‘applied linguistics’. I have shaped what follows partly in order to avoid excessive overlap with other chapters in this volume, and have therefore said relatively little about some matters which are dealt with in detail elsewhere. I begin by discussing brieﬂy what grammar is, why languages need it and how they use it. This is followed by a word on the remarkable proliferation of grammatical models in present-day linguistic theory, and a note on the relationship, such as it is, between these models and applications of linguistics. I then look brieﬂy at applied linguistics at its most ambitious: the period when it was believed that investigating the nature of language would inform us about the world; and at later oﬀshoots of this line of thought. A short note on the language-mind-brain relationship is followed by two more extensive sections, on grammar in mother tongue education and foreign language teaching, respectively.