Drawing on data from the Swiss Household Panel (SHP), we examine first union formation among immigrants and their descendants by comparing their behaviour to thatof the ‘native’ population in Switzerland. The empirical evidence shows that there are differences in the timing of union formation between immigrantsand the Swiss natives. Within the immigrant group, we also observe differences between those who arrived in Switzerland as adults and their descendants, who have been born or socialized in Switzerland from very early ages. The formation of a first union amongthe descendants of immigrants occurs later than among immigrants. This supports the adaptation (integration) hypothesis: through generations, social norms of the host country are adopted and integrated in union behaviour of individuals with a migrant background.