This volume offers an overview of current research on grammatical number in language. The chapters Part i of the handbook present foundational notions in the study of grammatical number covering the semantic analyses of plurality, the mass–count distinction, the relationship between number and quantity expressions and the mental representation of number and individuation. The core instance of grammatical number is marking for number distinctions in nominal expressions as in English the book/the books and the chapters in Part ii, Number in the nominal domain, explore morphological, semantic, and syntactic aspects of number marking within noun phrases. The contributions examine morphological marking of number the relationship between syntax and nominal number marking, and the interactions between numeral classifiers with semantic number and number marking. They also address cases of mismatches in form and meaning with respect to number displayed by lexical plurals and collective nouns. The final chapter reviews nominal number processing from the perspective of language pathologies. While number marking on nouns has been the focus of most research on number, number distinctions can also be found in the event domain. Part iii, Number in the event domain, presents an overview of different linguistic means of expressing plurality in the event domain, covering verbal plurality marking, pluractional modifiers of the form Noun preposition Noun, frequency adjectives and dependent indefinites. Part iv provides fifteen case studies examining different aspects of grammatical number marking in a range of typologically diverse languages.