This systematic review surveyed research on the associations between sleep and the memory processes involved in word learning in infancy. We found only 16 studies that addressed this topic directly, identifying associations between infant sleep and the memory processes, the identification of word forms in running speech, and the stabilization and generalization of new word form-meaning associations. Some studies investigated changes in brain responses after word learning and in sleep parameters during postlearning sleep. Others investigated the long-term effects of sleeping patterns on later vocabulary development. All but one of these studies identified positive associations between sleep and word learning in early childhood, extending similar findings from studies on adults and school-aged children. However, there remain several gaps in the current research on early lexical development and sleep. Future investigations should address these gaps for researchers to better understand lexical development and to create links between memory and language acquisition research.