King of Sumer and Akkad was a royal title in Ancient Mesopotamia combining the titles of "King of Akkad", the ruling title held by the monarchs of the Akkadian Empire with the title of "King of Sumer". The title simultaneously laid a claim on the legacy and glory of the ancient empire that had been founded by Sargon of Akkad and expressed a claim to rule the entirety of lower Mesopotamia. Despite both of the titles "King of Sumer" and "King of Akkad" having been used by the Akkadian kings, the title was not introduced in its combined form until the reign of the Neo-Sumerian king Ur-Nammu, who created it in an effort to unify the southern and northern parts of lower Mesopotamia under his rule. The older Akkadian kings themselves might have been against linking Sumer and Akkad in such a way.

Ur-Nammu founded the Sumerian Third Dynasty of Ur, in southern Mesopotamia, following several centuries of Akkadian and Gutian rule. His main achievement was state-building, and Ur-Nammu is chiefly remembered today for his legal code, the Code of Ur-Nammu, the oldest known surviving example in the world. He held the titles of "King of Ur, and King of Sumer and Akkad".