For decades researchers have studied how people with a migration background integrate into ethnic majority societies. Now that the ethnic majority has become a local numerical minority, this dissertation flips the question: how do people without a migration background integrate into majority-minority contexts and why do particular variations in integration outcomes emerge? The research question is answered in four empirical chapters which are based on data stemming from a mix of quantitative and qualitative methods: a large-scale international survey (n = 2,457), semi-structured face-to-face interviews (n = 20) and a vignette survey experiment (n = 364). When defined as a two-dimensional concept with ‘attitude towards ethnic diversity’ and ‘behaviour in form of inter-ethnic contact’, the integration outcomes of people without a migration background are more complex than previously assumed. On the one hand, people without a migration background have different integration outcomes that go beyond merely polarised reactions. These outcomes vary as they are dependent on the socio-economic background and previous experience with diversity. On the other hand, the integration of people without a migration background does not happen without further effort. The employment of social strategies is necessary to become an integrated insider in spaces in which people without a migration background are a numerical ethnic minority. The implications of the results are two-fold. Firstly, some people without a migration background are better equipped than others to integrate into majority-minority contexts, but ‘doing’ ethnic diversity can be ‘learnt’. Secondly, existing theories on integration which had as their focus people with a migration background are insufficient to understand the particular social positions of people without a migration background in majority-minority contexts.