This chapter reviews the use of Aramaic throughout the Achaemenian empire. In the Achaemenian period Aramaic endorsements on cuneiform tablets increase in number, Aramaic words enter Akkadian, Aramaic expressions may often be traced in the Late Babylonian legal texts, and there are increased references in the texts to leather documents and to the sepiru who served as scribe, translator and expert. First evidence for the use of Aramaic in the eastern parts of the empire is the Arsham letters which provide an excellent example of the highly developed use of Aramaic for communication in the Achaemenian empire. During the Hellenistic period, when Greek took the place of Aramaic as the official language throughout much of the same geographic area, the uniformity of the Aramaic script gradually broke down. The Aramaic script was often called 'Assyrian'. The use of Aramaic script and Aramaic ideograms in the various Middle Persian dialects is an important result of the practice of Achaemenian chanceries.