Repetition is a central phenomenon of behavior, and researchers have made extensive use of it to illuminate psychological functioning. In the language sciences, a ubiquitous form of such repetition is "structural priming," a tendency to repeat or better process a current sentence because of its structural similarity to a previously experienced ("prime") sentence (J. K. Bock, 1986). The recent explosion of research in structural priming has made it the dominant means of investigating the processes involved in the production (and increasingly, comprehension) of complex expressions such as sentences. This review considers its implications for the representation of syntax and the mechanisms of production and comprehension and their relationship. It then addresses the potential functions of structural priming, before turning to its implications for first language acquisition, bilingualism, and aphasia. The authors close with theoretical and empirical recommendations for future investigations. (Contains 5 footnotes and 2 figures.)