Urmonotheismus (German for "primeval monotheism") or primitive monotheism is the hypothesis of a monotheistic Urreligion, from which non-monotheistic religions degenerated. This is diametrically opposed to the evolutionary view of religion, which holds that religion progressed from simple forms to complex: first preanimism, then animism, totemism, polytheism and finally monotheism (see Anthropology of religion).

Scottish anthropologist Andrew Lang concluded in 1898 that the idea of a high god or 'All Father' existed among some of the simplest of contemporary tribes, prior to Western contact.

It was first defended by Wilhelm Schmidt (1868–1954), in his Der Ursprung der Gottesidee appearing from 1912, opposing the "Revolutionary Monotheism" approach that traces the emergence of monotheistic thought as a gradual process spanning the Bronze and Iron Age Religions of the Ancient Near East and Classical Antiquity.

Alleged traces of primitive monotheism were located in the deities Assyrian Ashur and Marduk, and Hebrew YHWH. Monotheism in Schmidt's view is the "natural" form of theism, which was later overlaid and "degraded" by polytheism.