Akkadian (lišānum akkadītum, 𒀝𒂵𒌈 ak.kADû) (also Accadian, Assyro-Babylonian) is an extinct Semitic language (part of the greater Afroasiatic language family) that was spoken in ancient Mesopotamia. The earliest attested Semitic language, it used the cuneiform writing system, which was originally used to write ancient Sumerian, an unrelated language isolate. The name of the language is derived from the city of Akkad, a major center of Semitic Mesopotamian civilization, during the Akkadian Empire (ca. 2334–2154 BC), although the language predates the founding of Akkad.

The mutual influence between Sumerian and Akkadian had led scholars to describe the languages as a sprachbund.
Akkadian proper names were first attested in Sumerian texts from ca. the late 29th century BC. From the second half of the third millennium BC (ca. 2500 BC), texts fully written in Akkadian begin to appear. Hundreds of thousands of texts and text fragments have been excavated to date; covering a vast textual tradition of mythological narrative, legal texts, scientific works, correspondence, political and military events, and many other examples. By the second millennium BC, two variant forms of the language were in use in Assyria and Babylonia, known as Assyrian and Babylonian respectively.

Akkadian had been for centuries the lingua franca in Mesopotamia and the Ancient Near East. However, it began to decline around the 8th century BC, being marginalized by Aramaic during the Neo Assyrian Empire. By the Hellenistic period, the language was largely confined to scholars and priests working in temples in Assyria and Babylonia. The last Akkadian cuneiform document dates to the 1st century AD. A fair number of Akkadian loan words survive in the Mesopotamian Neo Aramaic dialects spoken in and around modern Iraq by the indigenous Assyrian (aka Chaldo-Assyrian) Christians of the region, and the giving of Akkadian personal names, along with a number of Akkadian last names and tribal names, is still common amongst Assyrian people.