The people of Mesopotamia believed in many gods and goddesses. These represented natural features, the forces of nature and the heavenly bodies. From the middle of the third millennium B.C. representations of the gods show them in human form but wearing a horned crown or helmet. This may be an attempt to link the deities to the power of nature. They are often accompanied by their sacred animals and symbols. Each settlement had its own patron deity and divine family. There were also tribal, family and personal gods and goddesses. Each person was believed to have their own protective god and goddess. If these deities decided to abandon a person it could result in illness or misfortune. Spells, prayers and rituals were designed to maintain the blessings of the gods. It was possible to divine the will of the gods through special rites such as extispicy (the taking of omens) and astrology. The gods lived in temples where their statues were washed, clothed and fed. During festivals the divine statues were carried in processions. Few divine images survive since the most important examples would have been made of precious materials and were often broken up when captured by invading armies. Occasionally, enemy kings would keep a god's statue hostage and only return it to its temple when political conditions were favourable.

There is very little information about Mesopotamian ideas about death and an afterlife. A few poetic descriptions of the underworld survive. It is a dark place where the dead wander like shadows and is organised like a kingdom ruled over by the goddess Ereshkigal and her husband Nergal. Conditions were made better for the dead if the living provided them with offerings of food and drink. Alternative views of an afterlife may be suggested by the Royal Graves of Ur where the sacrificial victims may have been thought to accompany the main occupant of the tomb to a next life (although there is nothing to prove this and the graves are unique in Mesopotamia). The tombs of some of the queens of Assyria have been discovered at Nimrud where the bodies were surrounded with astonishing jewellery and other exotic goods. A cuneiform text in one of the tombs curses anybody who disturbs the body.