the fairly uniform Hellenistic Greek spoken and written from the 4th century BC until the time of the Byzantine emperor Justinian (Justinian I) (mid-6th century AD) in Greece, Macedonia, and the parts of Africa and the Middle East that had come under the influence or control of Greeks or of Hellenized rulers. Based chiefly on the Attic dialect, the Koine had superseded the other ancient Greek dialects by the 2nd century AD. Koine is the language of the Greek translation of the Old Testament (the Septuagint), of the New Testament, and of the writings of the historian Polybius and the philosopher Epictetus. It forms the basis of Modern Greek. See also Greek languages (Greek language).

The divergences of the Koine from classical norms gave rise in the 1st century AD to a purist movement known as Atticism, which had little effect on the everyday spoken language although it influenced the written language, causing it to have archaizing tendencies.