Culture erosion, threats to national identity and notions of “us vs. them” often figure directly or indirectly in the discourse of opponents to immigration. The extent of these non-economic concerns largely depends on how well immigrants can integrate socially, where social integration can be understood from two perspectives. For immigrants, it means developing a sense of belonging to the host society. This often involves accepting and acting according to that society’s values and norms and, if necessary, building up the social capital that is deemed necessary by the host country’s institutions. The role of the native population is equally important: social integration is only feasible once immigrants are accepted as members of the society. Such mutual recognition, apart from improving individual well-being, leads to better social cohesion and has considerable economic implications, from the provision of public goods and redistribution to team-work and productivity in firms. Yet, if immigrants and the native population differ in many social and cultural dimensions, social integration poses a challenge. Understanding the determinants of social integration and how to facilitate it thus represents a policy-relevant research area.