Drawing on new evidence from Hungarian, this book offers a closely integrated semantic and syntactic analysis and sheds new light on the behaviour of FCIs in a number of previously unexamined but crucial environments and constructions. Such an approach proves especially fruitful since in Hungarian, information structure and operator scope is to a large extent reflected in overt syntactic structure. Based on this, the book offers a detailed and insightful analysis of FCIs in identificational focus and contrastive topic position, and explores the fine scope interactions of FCIs and operators such as universal quantifiers, negation and focus. The monograph also provides a new account of the licensing of FCIs in (weak) imperatives which has significant implications for the formal semantics and pragmatics of imperatives. The generally unchallenged assumption that FCIs are cross-linguistically licensed in generics is also revisited and critically evaluated. The book provides a comparative analysis of referentially vague items and FCIs and concludes with a diachronic analysis of the emergence of FCIs in Hungarian.