This work examines both historical and comparative evidence in documenting the sweep of diachronic change in the context of serial verb constructions. Using a wide range of data from languages of West Africa, Asia and the Caribbean, it demonstrates how shifts in meaning and usage result in syntactic, morphological and lexical change. The process by which verbs lose lexical semantic content and develop case-marking functions is described; it is argued that the change is directional, from verb to preposition (or postposition) to affix, along a grammaticalization continuum. This same grammaticalization process is shown to result in the development of complementizers, adverbial subordinators, conjunctions, adverbs and auxiliaries from verbs. Strong parallels across languages are found in the meanings of the verbs that become “defective” and in the functions they come to mark. The changes are documented in detail, with examples from a number of languages illustrating the effect of the changes on typology and word order, implications for the encoding of definiteness and aspect, and the relevance of notions such as discourse topic, foreground and transitivity. With respect to theoretical assumptions and terminology, the author has taken a relatively nonpartisan approach, and the discussion is accessible to students of language as well as of interest to theoreticians.