This article investigates the role religious beliefs play in leading European Muslims to justify terrorism, using survey data collected in twenty-one countries. Results show that the factors leading Muslims to justify terrorism contextually vary. Where Muslims are predominant, this probability decreases with the importance respondents assign to religion, while it increases where Muslims are a minority. We find no evidence in support of the thesis that Islamist propaganda causes ordinary believers' radicalization. Yet, in Western countries affected by homegrown terrorism, we observe that justifying terrorism is strongly associated with an increase in religious practice, providing support to the thesis that Islamist groups are attracting Islam radical individuals.