This study examines how exposure to foreigners shapes immigration attitudes. Despite decades of research and many valuable contributions, the empirical evidence remains inconclusive, reflecting a broader theoretical divide between group threat (Blumer 1958) and contact theories (Allport 1979). This paper introduces a new theoretical framework that reconciles the existing contradictory findings. It proposes that while an increased presence of foreigners diminishes local support for immigration, early exposure to diversity moderates this effect. It further hypothesises that such exposure during childhood and adolescence fosters positive intergroup relations later in life, whereas sustained exposure in adulthood may not mitigate the negative effects. To test these hypotheses, the paper leverages fine-grained geolocalised panel data from Switzerland (1999-2020) and the Czech Republic (2015-2019). It offers several innovative operationalisations of early socialisation and habituation, spanning from individuals’ exposure to foreigners during their formative years at the municipal level to geographic proximity to high-exposure areas, such as major urban centres and cross-border regions. The results show that the presence of foreigners in respondents’ localities of residence exerts an immediate negative effect on their support for immigration. Interestingly, locals who grew up in areas with a higher presence of foreigners are less likely to react negatively to the new influx. By contrast, prolonged exposure to foreigners in adulthood does not moderate the negative effect of exposure. These findings carry important implications for our understanding of how exposure and early socialisation affect intra-group relations, shedding light on the long-term impact of demographic shifts on immigration attitudes.