This Element provides an overview of structural priming research across the three main populations on which experimental priming studies have concentrated: adult monolingual speakers, first language learners, second language learners, and bilinguals. Priming studies with monolingual adults were originally designed to inform psycholinguistic models of grammatical encoding in language production. Thanks to the the implicit nature of the task, priming has turned out to be suitable for experimentally addressing questions about linguistic representation and use at the sentence level in speakers of any age. The view that priming is a form of implicit learning has sparked an interest in exploring continuity and life-long learning in language, opening up rich research areas in second language acquisition and bilingualism. Priming rightly deserves to be a part of every language scientist's tool kit.