Employing a comparative experimental design drawing on over 18,000 interviews across eleven countries on four continents, this article revisits the discussion about the economic and cultural drivers of attitudes towards immigrants in advanced democracies. Experiments manipulate the occupational status, skin tone and national origin of immigrants in short vignettes. The results are most consistent with a Sociotropic Economic Threat thesis: In all countries, higher-skilled immigrants are preferred to their lower-skilled counterparts at all levels of native socio-economic status (SES). There is little support for the Labor Market Competition hypothesis, since respondents are not more opposed to immigrants in their own SES stratum. While skin tone itself has little effect in any country, immigrants from Muslim-majority countries do elicit significantly lower levels of support, and racial animus remains a powerful force.The explosive rise in immigration worldwide over the last two decades has led to significant changes in the demographic composition of many developed countries. The political consequences of these shifts are profound, including the formation and electoral success of anti-immigrant parties in Western Europe, the passage of the UK's referendum to leave the European Union, and now President Trump's drive to dramatically tighten US immigration policy after his election in 2016. Debates about threats posed by immigrants have become a regular feature of election campaigns, and were especially prominent in the 2016 US and 2017 Dutch elections. Then, as for many years before, political rhetoric about the issue was rife with cues highlighting both cultural differences between natives and newcomers, and the potentially negative economic consequences of increasing immigration. The causal antecedents of mass opinion about immigration have received some careful attention, but comprehensive, comparative analyses are still rare, and most such attempts are survey-based correlational studies rather than experiments that can isolate specific causal mechanisms. One core debate focuses on the economic versus ethno-cultural drivers of opposition to new immigrants in advanced industrial nations. In this article, we present results from the largest systematic, cross-national and controlled experimental study of these explanations to date.