How do plurals and mass nouns refer? What kind of logic should be used in order to account for the truth-conditions of the sentences they appear in? For linguists, first-order predicate logic is adequate, provided it is supplemented by a notion of mereological sum for plurals and for mass nouns. On the contrary, according to some philosophers, new logics must be used, plural logic for plurals and mass logic for mass nouns. We survey these debates in this entry.