Abstract
<jats:p>Grammaticalization and degrammaticalization are gradual, composite changes involving primitive changes on more than one linguistic level (syntax, morphology, phonology/phonetics, semantics, pragmatics). They are an important topic not only in diachronic linguistics, but also in linguistic typology and the study of language contact. Grammaticalization is very common in languages worldwide, with similar pathways (e.g., from body part noun to spatial adposition or from movement verb to future auxiliary) attested in many, often typologically unrelated languages. Grammatical items, in turn, have been attested to give rise to bound morphemes, such as tense or person inflections. Degrammaticalization, by contrast (the shift from a grammatical item to a lexical item or from a bound morpheme to a free one), is more rare, and not uncontroversial, but it puts important constraints on reconstruction of grammatical changes where diachronic data are not available. Finally, zooming out from the morpheme level to the more abstract level of morphological systems, (de)grammaticalization research also enhances our knowledge of cyclic change in morphological typology. This entry offers a classification of (de)grammaticalization changes and argues that their differences and similarities can be analyzed in a unified model that focuses on (clusters of) primitive changes, various approaches to (de)grammaticalization (diachronic, typological, constructionist), and outlines possible directions for future research into these phenomena.</jats:p>