The recent massive arrival of war refugees has challenged Europe’s political unity and fanned the flames of anti-Muslim populism. Both discourses have been framed in terms of ‘shifting solidarity’ between the European Union member states, their citizens and the refugees. At stake, the article argues, is the delineation of the collectivity linked by the obligation of solidarity. Drawing on insights from research conducted among Polish-born migrants in Germany about their practices and attitudes towards helping the refugees, and critically engaging with social theory, this article offers a new understanding of transnational solidarity. Transnational solidarity, it argues, needs to embrace the tension between cosmopolitan and particularistic ideas around belonging. The article suggests defining transnational solidarity as an outcome of socio-culturally and spatio-temporally specific interpretations of the norm of solidarity. As a heuristic device, transnational solidarity helps us to understand the shifting alliances for and against refugees in Europe.