High levels of worldwide migration paired with increasingly negative attitudes toward immigrants and immigration in host countries indicate that it is crucial to gain an understanding of the bases of these attitudes. This article discusses one determinant of negative attitudes toward immigrants and immigration: perceived competition for resources. We present our instrumental model of group conflict, which suggests that competition for resources, and attempts to remove this competition, are important determinants of intergroup attitudes and behavior. We then review relevant research on perceived competition and attitudes toward immigrants and immigration. We conclude by discussing the implications of this research for attempts to alleviate tension between immigrants and members of host populations, and for our more general model of group conflict.