Datasets in the field of ethnic politics still tend to treat ethnonational groups as unitary actors and do not differentiate between the positions of the organizations representing these groups. Datasets in the field of party politics differentiate between the positions of political parties, yet fail convincingly to conceptualize an ethnonational dimension of competition. This Research Note presents EPAC, a new dataset on Ethnonationalism in Party Competition that seeks to fill this gap. Based on an expert survey, EPAC provides cross-sectional data on the ethnonational positions of 210 political parties in 22 multinational European democracies. The conceptualization of an ethnonational dimension of competition underlying the dataset is introduced and a series of validity and reliability tests performed. Test results show that EPAC provides valid and reliable measures of party positions on an ethnonational dimension that can serve as an empirical base for study of the causes and effects of the mobilization of ethnicity in party competition.