Sin () or Suen (Akkadian: 𒀭𒂗𒍪, EN.ZU) also known as Nanna (Sumerian: 𒀭𒋀𒆠 ŠEŠ.KI, NANNA) is the Mesopotamian god representing the moon. While these two names originate in two different languages, respectively Akkadian and Sumerian, they were already used interchangeably to refer to one deity in the Early Dynastic period. They were sometimes combined into the double name Nanna-Suen. A third well attested name is Dilimbabbar (𒀭𒀸𒁽𒌓). Additionally, the name of the moon god could be represented by logograms reflecting his lunar character, such as 30 (𒀭𒌍), referring to days in the lunar month or U4.SAKAR (𒀭𒌓𒊬), derived from a term referring to the crescent. In addition to his astral role, Sin was also closely associated with cattle herding. Furthermore, there is some evidence that he could serve as a judge of the dead in the underworld. A distinct tradition in which he was regarded either as a god of equal status as the usual heads of the Mesopotamian pantheon, Enlil and Anu, or as a king of the gods in his own right, is also attested, though it only had limited recognition. In Mesopotamian art, his symbol was the crescent. When depicted anthropomorphically, he typically either wore headwear decorated with it or held a staff topped with it, though on kudurru the crescent alone serves as a representation of him. He was also associated with boats.
The goddess Ningal was regarded as Sin's wife. Their best attested children are Inanna (Ishtar) and Utu (Shamash), though other deities, for example Ningublaga or Numushda, could be regarded as members of their family too. Sin was also believed to have an attendant deity (sukkal), Alammuš, and various courtiers, such as Nineigara, Ninurima and Nimintabba. He was also associated with other lunar gods, such as Hurrian Kušuḫ or Ugaritic Yarikh.