Ninlil (𒀭𒎏𒆤 NIN.LÍL; meaning uncertain) was a Mesopotamian goddess regarded as the wife of Enlil. She shared many of his functions, especially the responsibility for declaring destinies, and like him was regarded as a senior deity and head of the pantheon. She is also well attested as the mother of his children, such as the underworld god Nergal, the moon god Nanna or the warrior god Ninurta. She was chiefly worshiped in Nippur and nearby Tummal alongside Enlil, and multiple temples and shrines dedicated to her are attested in textual sources from these cities. In the first millennium BCE she was also introduced to Ḫursaĝkalamma near Kish, where she was worshiped alongside the goddess Bizilla, who was likely her sukkal (attendant deity).
At an early date Ninlil was identified with the goddess Sud from Shuruppak, like her associated with Enlil, and eventually fully absorbed her. In the myth Enlil and Sud, Ninlil is the name Sud received after marrying Enlil. Nisaba, the goddess of writing, and her husband Haya are described as her parents. While Ninlil's mother bears a different name, Nunbaršegunu, in the myth Enlil and Ninlil, the god list An = Anum states that it was an alternate name of Nisaba. Syncretism with Sud also resulted in Ninlil acquiring some of her unique characteristics, such as an association with healing goddesses and with Sudaĝ, a name of the wife of the sun god Shamash. References to these connections can be found in various Mesopotamian texts, such as a hymn referring to Ninlil as a healing goddess or a myth apparently confusing her with Sudaĝ in the role of mother of Ishum.