Akkadian (, Akkadian: 𒀝𒅗𒁺𒌑 akkadû) is an extinct East Semitic language that was spoken in ancient Mesopotamia (Akkad, Assyria, Isin, Larsa and Babylonia) from the third millennium BC until its gradual replacement by Akkadian-influenced Old Aramaic among Mesopotamians by the 8th century BC.

It is the earliest documented Semitic language. It used the cuneiform script, which was originally used to write the unrelated, and also extinct, Sumerian (which is a language isolate). Akkadian is named after the city of Akkad, a major centre of Mesopotamian civilization during the Akkadian Empire (c. 2334–2154 BC). 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 around the mid 3rd-millennium BC. From about the 25th or 24th century BC, texts fully written in Akkadian begin to appear. By the 10th century BC, two variant forms of the language were in use in Assyria and Babylonia, known as Assyrian and Babylonian respectively. The bulk of preserved material is from this later period, corresponding to the Near Eastern Iron Age. In total, hundreds of thousands of texts and text fragments have been excavated, covering a vast textual tradition of mythological narrative, legal texts, scientific works, correspondence, political and military events, and many other examples.

Centuries after the fall of the Akkadian Empire, Akkadian (in its Assyrian and Babylonian varieties) was the native language of the Mesopotamian empires (Old Assyrian Empire, Babylonia, Middle Assyrian Empire) throughout the later Bronze Age, and became the lingua franca of much of the Ancient Near East by the time of the Bronze Age collapse c. 1150 BC. Its decline began in the Iron Age, during the Neo-Assyrian Empire, by about the 8th century BC (Tiglath-Pileser III), in favour of Old Aramaic. By the Hellenistic period, the language was largely confined to scholars and priests working in temples in Assyria and Babylonia. The last known Akkadian cuneiform document dates from the 1st century AD. Mandaic and Suret are two (Northwest Semitic) Neo-Aramaic languages that retain some Akkadian vocabulary and grammatical features.

Akkadian is a fusional language with grammatical case; and like all Semitic languages, Akkadian uses the system of consonantal roots. The Kültepe texts, which were written in Old Assyrian, include Hittite loanwords and names, which constitute the oldest record of any Indo-European language.