Sumerian religion was the religion practiced by the people of Sumer, the first literate civilization found in recorded history and based in ancient Mesopotamia. The Sumerians regarded their divinities as responsible for all matters pertaining to the natural and social orders.

Anu or Anum, originally An, was the divine personification of the sky, king of the gods, and ancestor of many of the deities in ancient Mesopotamian religion. He was regarded as a source of both divine and human kingship, and opens the enumerations of deities in many Mesopotamian texts. At the same time, his role was largely passive, and he was not commonly worshipped. It is sometimes proposed that the Eanna temple located in Uruk originally belonged to him, rather than Inanna, but while he is well attested as one of its divine inhabitants, there is no evidence that the main deity of the temple ever changed, and Inanna was already associated with it in the earliest sources. After it declined, a new theological system developed in the same city under Seleucid rule, resulting in Anu being redefined as an active deity. As a result he was actively worshipped by inhabitants of the city in the final centuries of the history of ancient Mesopotamia.