Almost 2 million people in the North and South of Ireland identify as Irish speakers and an estimated 70 million around the globe can claim Irish heritage. While Irish ancestry may be distant for many, the Irish language is active in numerous locations in the diaspora, as documented in research profiling communities across the globe (e.g. Callahan, 1994; Garland 2008; Giles 2016; Kallen 1984, 1994; Noone, 2012a; Ó hEadhra, 1998;Ó Conchubhair 2008; Walsh & NíDhúda 2015 inter alia) and evidenced by the existence of many cultural and language groups. Census figures indicate that at least25,000 people currently speak the language in Canada, the United States and Australia alone (Statistics Canada, 2013; United States Census Bureau, 2015; Australian Bureau of Statistics, 2012), yet very few in-depth general accounts of Irish-language use in the diaspora exist. Linguistic practices within Irish communities worldwide vary widely with regard to Irish-language use and language ideologies, with each community subject to distinct concerns, histories and discourses. As such, each has distinct possibilities for creating social and cultural meaning, possibilities that are fundamentally shaped by the socio-cultural and politico-historical contexts within which the Irish language has existed in the last 200 years. This paper investigates how the Irish language is recruited in constructions of cultural authenticity in three sites in the Irish diaspora: Boston, U.S.; Melbourne, Australia; and St. John’s, Newfoundland, Canada. Research is based on open-ended qualitative interviews with 41 learners and speakers regarding the Irish language and their own language practices, and in extensive participant observation of cultural and language-related activities in each site. Thematic content analysis of interview data provides the basis for ethnographic descriptions of each site. A Foucauldian understanding of discourse (e.g. Pennycook, 1994; Foucault, 1981, 1972) affords the identification and delineation of predominant discourses within which Irish-language use is implicated as a meaningful social act, and that are enacted or actively resisted within and across communities, as well as key subject positions made available within these discourses. This approach provides the basis for an exploration of (i) the processes of authenticating a cultural practice within discourse; (ii) how such processes shape the changing configurations of who is included and who is excluded within dominant politico-cultural discourses; and (iii) the various formations of community that exist within and across the diaspora space. The paper shows that the role of the Irish language in authenticating Irish cultural identity is subject to reworkings across time and space, as exemplified in the variety of local meanings it has taken on across the three diaspora sites featured.