The paper advances our empirical and theoretical understanding of migrant assimilation. It does so by focusing on a very particular group of individuals who appear more likely than other migrant types to "go native." We call these individuals "mixed nationality relationship migrants" ( i.e. , migrants who have committed to a life outside their home country because of the presence of a foreign partner). The paper argues that the transnational family milieus that emerge from this form of international migration are critical to the assimilation process. Empirical material from 11 in-depth interviews with female migrants in Britain (Sheffield) and France (Paris) supports our argument. We also suggest that such "extreme" assimilation is more likely within a regional migratory system -like the EU -where the "identity frontiers" crossed in the formation of a transnational family are relatively shallow.