Language users are creatures of habit with a tendency to re-use linguistic material that they have produced or heard before. In other words, linguistic patterns and tokens, once used, persist in spoken discourse. The book explores the determinants of this persistence in corpus data of spoken English, drawing on regression analyses of a variety of functional, discourse-functional, cognitive, psycholinguistic, and external factors. In providing a variationist-probabilistic framework for examining the ways in which different internal and external factors influence speakers' linguistic choices, the study ultimately contributes to a theory of how spoken language works.