This dissertation seeks to add to the understanding of ethnic tensions. It does so by exploring in a four-part study one of its most important but severely overlooked features: language. Combining research traditions from sociolinguistics, social psychology and political science, this dissertation provides an in depth analysis of language’s influence on intergroup relations. It does so, specifically, by concentrating on the influence that linguistic vitality, the social health of a language, has on social tensions. This dissertation puts forward a theoretical framework in which linguistic vitality is presented as fueling cultural grievances, which subsequently impact intergroup relations. The first article explores the general macro-social relationship between linguistic vitality and intergroup conflict intensity. Using data from UNESCO’s Atlas of the World’s Languages in Danger and from the Minorities at Risk (MAR) project, the results show a curvilinear relationship in which low and high levels of linguistic vitality generate lower conflict intensity than moderate vitality levels. The findings support linguistic vitality as being an important determinant of language-based ethnic tensions in a general manner, but even more so for countries with multiple linguistic minorities. The second article explores the influence of linguistic vitality on political trust. The results of the analyses, using survey data from the European Social Survey (ESS) and linguistic vitality data from UNESCO’s Atlas of the World’s Languages in Danger, show that linguistic vitality positively influences trust in national institutions and that perceptions of linguistic discrimination decrease political trust. The findings further indicate that the status of a language, how ‘official’ it is, also positively affects trust in national institutions. Therefore, language is clearly underscored as being an important dimension of political trust. The third article seeks to isolate the socio-psychological sequence which connects linguistic vitality and intergroup tensions. Original survey data was gathered from Francophones in Quebec, Ontario, New Brunswick and Manitoba. The findings, using stepwise regression analyses, support a socio-psychological sequence in which in-group threat influences attitudes towards the out-group through the mediation of perceived threat caused by the out-group. Thus, these findings emphasize the importance of linguistic vitality perceptions on intergroup attitudes The fourth, and final, article, in collaboration with Patrick Fournier and Verònica Benet-Martínez, uses an experimental design to ascertain the causal role of linguistic vitality on intergroup attitudes. The results demonstrate that the type of information, positive or negative, on linguistic vitality influences perceptions of threat towards a language. However, results about linguistic vitality information’s impact on out-group attitudes, support for sovereignty and subjective identity were less one-sided. This dissertation permits to shine new light on group tensions by highlighting the important role that linguistic vitality plays on macro-social phenomena and micro-individual attitudes.