This paper studies the determinants of interethnic relationships between non-migrants and migrants in Germany. A large body of literature documents that such relationships generate positive outcomes for individual migrants as well as non-migrants and the social cohesion of host-societies at large. Previous research tends to focus on the migrant side, thereby neglecting the factors enabling non-migrants’ interethnic relationships. Moreover, the existing research on non-migrants exclusively uses cross-sectional data for causal inferences. In contrast, this paper draws on longitudinal data, thus providing a more comprehensive and empirically rigorous picture of the determinants of interethnic relationships. The paper identifies possible determinants of non-migrants’ interethnic relationships, combining them into a single analytical framework that allows for gauging their relative importance. Moderately high migrant shares in the neighbourhood are found to be connected to more interethnic relationships, while a higher share of foreigners in the wider region only has a positive effect for the employed. Neither employment status nor migrant share at work are found to be connected to non-migrants’ interethnic relationships. Finally, persons feeling threatened by immigration and migrants are largely found to be less likely to have interethnic relationships, while sympathy with migrants works in the opposite direction.