Chapter 23 reviews the role of grammaticalization at different levels of grammar: phonological, morpho-syntactic, paradigmatic, and semantic-pragmatic. It first discusses the dischronic principles and mechanisms that have been proposed in previous grammaticalization studies. The chapter then examines the prominent patterns by source category, dividing these into nouns and verbs. In the nominal category, four source construction types are illustrated with the reanalyses that led to their emergence as grammatical forms such as postpositions, conjunctions, and auxiliaries. In the verbal category, four source construction types are illustrated, with special focus on the grammaticalization of de-verbal postpositions and auxiliary verbs. The chapter further addresses select aspects of Korean grammaticalization from a typological perspective. It discusses the productive use of affixes, converbs, and predicatives known as “mermaid constructions”, which are among the characteristics shared by many languages in the eastern Eurasian region. It also discusses the presence of large inventories of de-verbal postpositions and numeral classifiers.