How can the world''s religions, which propagate peace and love, promote violence and the killing of innocent civilians through terrorist acts? This Element aims to provide insights into this puzzle by beginning with a brief overview of debates on terrorism, a discussion on religion and the various resources it provides groups engaging in terrorist acts, four arguments for what causes religious terrorism, brief examples of religious terrorism across faith traditions, and a synopsis of deradicalization programs. This discussion shows that, when combined with certain political and social circumstances, religions provide powerful resources for justifying and motivating terrorist acts against civilians.