Is American foreign policy Islamophobic? This dissertation examines that question by analyzing elite and mass attitudes through a multi-method empirical design. I draw on a longitudinal study of the United States Commission on International Religious Freedom (USCIRF) from 1999 to 2023, nationally representative data from the 2021 Collaborative Multiracial Post-Election Survey, and an original survey experiment to identify Islamophobic attitudes and their relationship to adverse foreign policy decisions. The analysis reveals substantial religious bias, particularly Islamophobia, in elite decisionmaking and organizational outputs. I argue that these patterns reflect broader prejudices in American society that manifest at individual, group, and institutional levels. Empirically, I show that USCIRF is more likely to recommend Muslim-majority states for punitive religious-freedom designations than non-Muslim states, even when the latter are implicated in comparable or graver violations, consistent with organizational Islamophobia. At the mass level, I find that public attitudes toward Muslim victims of foreign conflicts can be less sympathetic than attitudes toward non-Muslim groups, although some expectations about sanctions and humanitarian concern yield mixed results. Theoretically, the dissertation advances a new typology of Islamophobia that distinguishes multiple forms of bias—high-cost and low-cost manifestations and implicit versus explicit cycles of hostility—and situates them within broader processes of elite socialization, nationalism, and cognitive prejudice. Taken together, the findings underscore the need for renewed attention to Islamophobia in U.S. foreign policy and for an analytical lens that looks beyond high politics to include bureaucratic outputs and everyday public attitudes.