Sumerian (𒅴𒂠 EME.ĜIR₁₅ "native tongue") is the language of ancient Sumer, which was spoken in southern Mesopotamia (modern Iraq) since at least the 4th millennium BC. During the 3rd millennium BC, there developed a very intimate cultural symbiosis between the Sumerians and the Akkadians, which included widespread bilingualism. The influence of Sumerian on Akkadian (and vice versa) is evident in all areas, from lexical borrowing on a massive scale, to syntactic, morphological, and phonological convergence. This has prompted scholars to refer to Sumerian and Akkadian in the third millennium as a Sprachbund.

Akkadian gradually replaced Sumerian as a spoken language somewhere around the turn of the 3rd and the 2nd millennium BC (the exact dating being a matter of debate), but Sumerian continued to be used as a sacred, ceremonial, literary and scientific language in Mesopotamia until the 1st century AD. Then, it was forgotten until the 19th century, when Assyriologists began deciphering the cuneiform inscriptions and excavated tablets left by these speakers. Sumerian is a language isolate.