This study focuses on ethnic competition as a contextual explanation of cross-national differences in anti-immigrant prejudice. It contributes to the existing literature by refining the concept of ethnic competition into a socio-economic and a cultural aspect, which is reflected in two different measures of outgroup size. To improve cross-national comparability, the outgroup size measure is based on foreign country of birth instead of citizenship. Moreover, as outgroup size does not only measure competition, but also contact opportunities and familiarity with immigration, intergroup contact theory is taken into account and a non-linear relationship between outgroup size and perceived ethnic threat is tested. This study employs multi-level linear regression and uses the first round data set of the European Social Survey. The main conclusions of this analysis are that economic and social competition between groups might play a lesser role in the explanation of cross-national differences in anti-immigrant attitudes than often assumed, and that it might be rather lacking familiarity and fear of conflict over values and culture that drive the relationship between outgroup size and anti-immigrant attitudes.