This Element explores the relation between monotheism and fundamentalism. It does so from both an empirical perspective and a more theoretical one that combines theological and philosophical insights. The empirical part addresses how as a matter of fact, particularly quantitively, monotheism and fundamentalism relate to one another. The more theoretical part studies the relation between the two by considering the doctrine of God and the issue of exclusion, theories of revelation, and ethics. Finally, the book considers whether monotheism has particular resources that can be employed in mitigating the consequences of or even altogether preventing fundamentalism. This title is also available as Open Access on Cambridge Core.