Ninkasi was the Mesopotamian goddess of beer and brewing. It is possible that in the first millennium BC she was known under the variant name Kurunnītu, derived from a term referring to a type of high quality beer. She was associated with both positive and negative consequences of the consumption of beer. In god lists, such as the An = Anum list and the Weidner god list, she usually appears among the courtiers of the god Enlil, alongside deities such as Ninimma and Ninmada. She could also be paired with Siraš, a goddess of similar character, who sometimes was regarded as her sister. A possible association between her and the underworld deities Nungal and Laṣ is also attested, possibly in reference to the possible negative effects of alcohol consumption.

A number of works of Mesopotamian literature refer to Ninkasi, for example the myths Lugalbanda in the Mountain Cave and Lugalbanda and the Anzud Bird. A hymn dedicated to her, known simply as the Hymn to Ninkasi, is also known. It is commonly discussed and quoted in modern literature.

Ninkasi's name, written in cuneiform as ^dNin-ka-si, means "mistress of beer." The explanation "lady who fills the mouth" has been proposed in the past but according to Reallexikon der Assyriologie und Vorderasiatischen Archäologie should be considered implausible. A possible earlier writing of the name, ^dNin-^ka₁₅kaš-si, has been tentatively translated as "mistress barmaid," though its precise etymology remains a matter of debate. Like many other names of deities originating in the Sumerian language, it is assumed to be a combination of the grammatically neutral word nin, which appears in names of both male and female deities, and the name of a product, place or object. In one of the earliest Mesopotamian god lists, some forty percent of the deities have names starting with nin.

It has been proposed that the deity ^dKAŠ.DIN.NAM should be understood as a late form of Ninkasi. A second attested spelling of this name is ^dKAŠ.DIN.NU. The Sumerian compound KAŠ.DIN represents the word kurun (Akkadian: kurunnum), a type of beer regarded, in Mesopotamian texts, as being of a particularly high quality . According to Paul-Alain Beaulieu, the name was most likely read as Kurunnītu, though Kurunnam has also been proposed. Beaulieu considers the former option to be more likely, as the syllabic spelling ^dku-ru-ni-tu₄ is also attested. The equivalence between this deity and Ninkasi is directly attested in two lamentations.

Ninkasi was the goddess of beer, and as such was associated with its production, consumption and effects - both positive and negative. Jeremy Black described her as "one of (...) minor deities without a strongly defined personality who merely symbolise the object or phenomenon that they are associated with." While he also described her as a divine barmaid, Manfred Krebernik [de] argues that she was not connected with the sale of beer and with professions related to it.

The proposal that Ninkasi was also associated with wine, common in older literature, is no longer regarded as plausible.

While typically regarded as a goddess, in some late sources Ninkasi could appear as a male deity, a phenomenon also attested in the cases of the artisan goddess Ninmug and Ninshubur, the sukkal (attendant deity) of Inanna.

It is possible that in art Ninkasi was depicted holding a cup. Furthermore, she might be among the deities shown in banquet scenes on items such as gaming boards and fragments of musical instruments.