Twenty years after 9/11, the impact of terrorism on social and political attitudes remains unclear. Several large-scale surveys suggest that terrorism has no discernible effects on direct, self-report measures of prejudice toward Arab-Muslims. However, direct measures may lack the sensitivity to detect subtle underlying attitudes that are considered socially unacceptable to openly express. To tap these subtle reactions, we assessed more sensitive and implicit measures of the cognitive–affective aspects of prejudice. Building on the justification–suppression model of prejudice, we hypothesized that terrorist attacks increase implicit bias toward Arab-Muslims, especially among individuals who are unable to regulate automatic hostile reactions due to personality or situational variables. Study 1, using data from Project Implicit (N = 276,311), showed that terrorist attacks increased implicit bias but not expressed prejudice toward Arab-Muslims. Study 2, using data from Google Trends, showed that terrorist attacks increased anti-Islamic searches on the internet. Four studies that collected original data (total N = 851) showed that the effects of reminders of terrorism on anti-Islamic implicit bias are moderated by individual differences in prejudice and automaticity (Studies 3–4), by the strength of implicit Muslim–terrorist associations (Study 5), and by momentary self-control depletion (Study 6). Overall, the present research indicates that despite little evidence for elevated overt expression of prejudice against Arab-Muslims following terrorist attacks, terrorist attacks increase anti-Islamic implicit bias whenever individuals are unlikely to control automatic hostile reactions.