In Sumerian mythology, Nammu is probably the first of the ancient deities of Sumer — at least in the process of Creation, if not in actual chronology. She was the goddess of the primeval sea that gave rise to heaven and earth, making her also the goddess of creation. She personifies the Apsu, or the sweet fertile waters, as the source of water and therefore fertility. She is both mother of all the gods and wife of An. Nammu is the goddess who had the idea of creating mankind as assistance for the gods.

After the Sumerian mythology, around the year 4000 BC (date agreed by most of specialists and beginning of the Sumerian area), a Sumerian couple lived in Dilmun (identified today as the isle of Bahrain): Nammu and her husband An.

After her death, Nammu became the Goddess of the sea (abzu) and An became the God of the Sky. Nammu was the mother and ancestor of all the Sumerian gods. Nammu will be later called : Ningal and An : Nanna (their Akkadian names).