Kassites (Akkadian Kashshū; Greek Cossaioi or Cissioi), people of ancient southwestern Asia. Early in the 17th century bc they invaded and settled much of the northern regions of Babylonia. About 1600 or 1595 bc the Hittites attacked Babylonia, weakening its military power. Subsequently, the Kassites captured Babylon and established a new dynasty that ruled southern and eastern Mesopotamia for the next four and one-half centuries. The Kassites adopted the Babylonian language and culture during that period and were virtually absorbed by the native population. About 1225 bc the Assyrian king Tukulti-Ninurta I captured Babylon and greatly weakened the political power of the Kassite dynasty. The Kassites, however, remained on the throne of Babylonia until about 1155 bc. They were conquered by Shutruk-Nahhunte I, king of Elam, who placed his own son on the throne.

Except for the names of numerous persons, places, and deities, historians know very little of the Kassite language. Scholars believe, however, that it was neither an Indo-European nor a Semitic language.

See also Elam.