Shamash (Akkadian Šamaš "Sun") was a native Mesopotamian deity and the sun god in the Akkadian, Assyrian and Babylonian pantheons. Shamash was the god of justice in Babylonia and Assyria, corresponding to Sumerian Utu. Akkadian šamaš is cognate to Syriac ܫܡܫܐ šemša or šimšu Hebrew שֶׁמֶשׁ šemeš and Arabic شمس šams.

Both in early and in late inscriptions Shamash is designated as the "offspring of Nannar"; i.e. of the moon-god, and since, in an enumeration of the pantheon, Sin generally takes precedence of Shamash, it is in relationship, presumably, to the moon-god that the sun-god appears as the dependent power. Such a supposition would accord with the prominence acquired by the moon in the calendar and in astrological calculations, as well as with the fact that the moon-cult belongs to the nomadic and therefore earlier stage of civilization, whereas the sun-god rises to full importance only after the agricultural stage has been reached.

The two chief centres of sun-worship in Babylonia were Sippar, represented by the mounds at Abu Habba, and Larsa, represented by the modern Senkerah. At both places the chief sanctuary bore the name E-barra (or E-babbara) "the shining house"—a direct allusion to the brilliancy of the sun-god. Of the two temples, that at Sippara was the more famous, but temples to Shamash were erected in all large centres – such as Babylon, Ur, Mari, Nippur, and Nineveh.