This paper addresses a contradiction in research on language and ethnicity: how can we discuss distinctively ethnic ways of speaking and still account for the variation and fluidity that characterize them? The theoretical construct introduced in this paper enables researchers to avoid this contradiction. ‘Ethnolinguistic repertoire’ is defined as a fluid set of linguistic resources that members of an ethnic group may use variably as they index their ethnic identities. This construct shifts the analytic focus from ethnic ‘language varieties’ to individuals, ethnic groups, and their distinctive linguistic features. It addresses problems of inter-group, inter-speaker, and intra-speaker variation, as well as debates about who should be considered a speaker of a dialect. This approach, which can also be applied to social groupings beyond ethnicity, is discussed in relation to other approaches and is supported with data on language use in African American, Latino, and Jewish communities in the United States.