Abstract
<jats:p> For the last 30 years, the concept of exaptation has been widely used to describe processes of language change that seem to run counter to typical grammaticalization paths. Classic examples involve the evolution of the English possessive marker ‐ <jats:italic>'s</jats:italic> or the refunctionalization of PIE ablaut alternations as tense and number markers in Germanic verbs. The notion of exaptation has its origin in evolutionary biology, where it is used to describe the process by which a part of an organism is used for a function for which it was not originally intended by natural selection. This concept was taken over into linguistics by Roger Lass in 1990. Here, it is mainly applied to processes of change that affect eroded language material that is assigned a new function. A process closely related to exaptation is ‘secretion’. Here a sound sequence within a holistic unit is reanalyzed as having a particular meaning and is thus used as the basis for the creation of a new affix, as ‐ <jats:italic>burger</jats:italic> in <jats:italic>hamburger</jats:italic> or ‐ <jats:italic>scape</jats:italic> in <jats:italic>landscape</jats:italic> . Apart from describing the concept of exaptation in detail, this chapter illustrates it with a variety of examples from various languages, not only at the morphological level where it is originally and mainly applied, but also at the levels of phonology, syntax, pragmatics, and the lexicon. Finally, exaptation is related to other language change processes such as grammaticalization, reanalysis, and analogy, and is also distinguished from similarly oriented language change processes, such as (re)functionalization, secretion, lateral conversion, or phonogenesis. </jats:p>