This study uses a field experiment to study bias against living with Arab American women, a group whose position in the U.S. race system remains uncertain. We developed fictitious female white and Arab American identities and used the audit method to respond to 560 roommate-wanted advertisements in four metro areas: Los Angeles, New York, Detroit, and Houston. To focus on social—rather than purely economic—biases, all responses identified the sender as college-educated and employed and were written in grammatically correct English. We compare the number of replies received, finding that Arab-origin names receive about 40 percent fewer replies. We then model variation in discrimination rates by proximity to mosques, geographic concentration of mosques, and the percentage of Arabs living in a census tract so as to test ethnic competition theory and the contact hypothesis. In Los Angeles and New York, greater discrimination occurred in neighborhoods with the highest concentration of mosques.