This book revisits the theoretical and psycholinguistic controversies centred around the intriguing nature of idioms and proposes a more systematic cognitive-linguistic model of their grammatical status and use. Whenever speakers vary idioms in actual discourse, they open a linguistic window into idiomatic creativity – the complex cognitive processing and representation of these heterogeneous linguistic constructions. Idiomatic creativity therefore raises two challenging questions: What are the cognitive mechanisms that underlie and shape idiom-representation? How do these mechanisms define the scope and limits of systematic idiom-variation in actual discourse? The book approaches these problems by means of a comprehensive cognitive-linguistic architecture of meaning and language and analyses them on the basis of corpus-data from the British National Corpus (BNC).