European empires experienced widespread anti-colonial rebellions during the First World War. These rebellions occurred for many different reasons, reflecting the diversity of context and history across colonial societies in Africa and Asia. Religion naturally played a strong role in most of the anti-colonial rebellions during the First World War, most prominently Islam. This article looks at the role Islam played in two key anti-colonial rebellions in North and West Africa: the rebellions in Batna, Algeria, and the Kaocen War in Niger, respectively. The article examines how Islam was instrumentalized by rebels, imperial collaborators, and French officers and administrators to further their own ends. Rebels called upon Islam to help inspire anti-colonial movements, to bind together diverse populations, and to contextualize their actions in wider socio-political conflicts. Imperial collaborators likewise called on religious authority to assist with European imperial recruitment efforts. French officers and administrators used Islam both as a justification and a target for collective punishment and repression after the rebellions were put down from 1917. This repression is still under-studied in a period usually portrayed as evidencing broad imperial harmony, rather than violent extraction and oppression.