Migration causes permanent processes of acculturation involving migrants but also members of mainstream society. A longitudinal field study with 70 German majority members investigated how their acculturation goals causally related to their attitudes and behaviours towards migrants. We distinguished acculturation goals concerning the migrants' culture(s) (what migrants should do) and acculturation goals concerning the usually neglected own changing mainstream culture. Both were conceived along the two dimensions of 'culture maintenance' and 'culture adoption'. Cross-sectionally we found many strong links between acculturation goals and attitudes and behaviours towards migrants, only some of which held longitudinally. As hypothesized there was no clear one-sided causal direction. As many causal links lead from acculturation goals to attitudes and behaviours, as in the opposite direction. Majority members' German culture acculturation goals proved especially valuable, because they determined attitudes and behaviour towards migrants most strongly.