Structural priming refers to speakers' tendency to produce sentences with previously heard or produced syntactic structures. We review arguments and evidence for three common accounts of the functions of structural priming. One is that structural priming enhances fluency. Only some (reaction time and fluency measure) evidence supports this view. A second account argues that structural priming stems from implicit learning of how features of meaning are linked to syntactic configurations. We describe evidence suggesting that structural priming exhibits effects characteristic of both learning and implicitness. A third account claims that structural priming is an aspect of coordination or alignment among interlocutors. Consistent with this, some evidence shows that structural priming involves a shorter-term component that is broadly sensitive to repeated bindings of wide-ranging types of knowledge. Together, these observations suggest that structural priming is likely a multifaceted force that reflects implicit learning and, possibly independently, alignment among interlocutors.