Recent research on political attitudes towards immigration often pits arguments emphasizing economic self-interest against ideological or cultural explanations. Many of these studies conceptualize immigration policy along a single dimension instead of disaggregating it into its distinct policy dimensions. Conditional on the type of immigration policy, different explanations should have more or less explanatory power. We disaggregate immigration policy into six different dimensions and provide theoretical scope conditions for when ideological and economic factors should matter. We test these predictions on votes on immigration policy in the US House of Representatives from 1979-2006. We advance the debate on the determinants of immigration policy by showing that both economic self-interest and ideological explanations can be powerful, depending upon the type of immigration policy under consideration.