This article theorizes the concept ‘ethnolinguistic infusion’ as a language socialization and language management practice. Infusion involves community members incorporating fragments of their group language, in which most members have little or no competence, in the context of a different dominant language, with the potential effect of fostering ideological links among the individual, group, and language. I explain the metaphor, enumerate several characteristics, and offer a categorization of different types of infusion. I contextualize ethnolinguistic infusion among related constructs in language contact, sociolinguistics, and linguistic anthropology, including translanguaging, postvernacularity, and metalinguistic communities, I explain its relationship to ethnolinguistic repertoire, and I distinguish it from out-group-initiated phenomena like crossing and mock language. I demonstrate how ethnolinguistic infusion plays out in my research on American Jewish summer camps. I offer empirical questions for future research, and I conclude by arguing for the utility of ethnolinguistic infusion, both for academic analysis and for language activism. (Language and ethnicity, heritage language, symbolic language, emblematic language, language and group identity, Hebrew, infusion, loanwords, language contact, translanguaging, metalinguistic community, postvernacularity, endangered languages, language reclamation, language revitalization)