Determiners are a nominal syntactic category distinct both from adjectives and nouns, despite the close affinity among them. They are commonly understood to comprise the word classes of article, demonstrative, and quantifier, as well as some possessives and some nominal agreement markers. Determiners became a prominent topic of study in grammatical theory during the 1980s, due both to advances in semantic theorizing, such as Generalized Quantifier Theory, and to the generalization of the X’ phrasal schema to minor (functional) categories, to which determiners are posited to belong. The main questions that have been the focus of theoretical and typological inquiry ever since are the categorial status of determiners (functional or lexical), whether they are universal as a distinct syntactic category, whether they constitute a uniform category or not, their structural position, their feature content, their role in argumenthood and semantic interpretation in general, and their relation to pronouns. Answers to these questions are, in part, determined by whether one takes determiners to be the nominal equivalent of complementizers (i.e., to constitute the topmost functional layer of the nominal phrase) or to be all quantifiers, defining relations between predicates. At the same time, a wealth of syntactic phenomena involving determiners have been investigated, shedding light not only on the structure of the nominal phrase and on the distribution of nominal features within it, but also on the nature of adjectives, possessives, and nouns.