Koine Greek is the popular form of Greek which emerged in post-Classical antiquity (c.300 BC – AD300), and marks the third period in the history of the Greek language. Other names are Alexandrian, Hellenistic, Common, or New Testament Greek. Koine is important not only to the history of the Greek people, for being their first common dialect and main ancestor of modern Greek but also for its impact on the Orthodox Church and the rest of the world. It was the original language of the New Testament of the Bible as well as the medium for the teaching and spreading of Christianity - unofficially the second language of the Roman Empire.
Biblical Koine refers to the varieties of Koine Greek used in the Bible and related texts. Its main sources are:
- the Septuagint;
- the New Testament, compiled originally in Greek (although some books may have had a Hebrew-Aramaic substrate and contain some Semitic influence on the language).
The term Patristic Greek is sometimes used for the Greek written by the Church Fathers, the early Christian theologians in late antiquity. Christian writers in the earliest time tended to use a simple register of Koiné, relatively close to the spoken language of their time, following the model of the Bible. After the 4th century, when Christianity became the official state religion of the Roman Empire, more learned registers of Koiné influenced by asceticism came also to be used.