This chapter has four main sections. It begins by discussing five anecdotes that highlight the role of religion in two types of large-scale violence: civil wars and terrorism. It then introduces key concepts, followed by important empirical facts about religious civil wars from 1940 to 2000. Finally, it examines religiously-inspired terrorism. Regarding both civil wars and terrorism, it is noted that religiously-inspired violence is, by and large, more deadly than violence justified by other means. In addition, it is shown that Islam has come to play a disproportionate role in violence: more than 80% of religious civil wars involve Islam, and religiously motivated incidents of terrorism involve Islam more than any other faith.