Lexicalization, a process of language change, has been conceptualized in a variety of ways. Broadly defined as the adoption of concepts into the lexicon, it has been viewed by syntacticians as the reverse process of grammaticalization, by morphologists as a routine process of word-formation, and by semanticists as the development of concrete meanings. In this up-to-date survey, Laurel Brinton and Elizabeth Traugott examine the various conceptualizations of lexicalization that have been presented in the literature, and propose a new, unified model of lexicalization in light of current work on grammaticalization.