The Septuagint ( /ˈsɛptjuːəˌdʒɪnt/), (/ˈsɛptuːəˌdʒɪnt/), (/ˌsɛpˈtuːədʒɪnt/), (/ˈsɛptʃuːəˌdʒɪnt/), (or "LXX", or "Greek Old Testament") is a translation of the Hebrew Bible and some related texts into Greek, begun in the late 3rd century BCE. The Septuagint is quoted by the New Testament (particularly by St. Paul), and by the Apostolic Fathers.
The traditional story is that Ptolemy II sponsored the translation for use by the many Alexandrian Jews who were fluent in Koine Greek (the lingua franca of the Eastern Mediterranean from the death of Alexander the Great in 323 BCE, until the development of Byzantine Greek around 600 CE), but not in Hebrew.
The Septuagint should not to be confused with the seven or more other Greek versions of the Old Testament, most of which do not survive except as fragments. (Some of these other Greek versions are known from Origen's Hexapla, a comparison of six translations in adjacent columns, now almost wholly lost.) Of these, the most important are "the three:" those by Aquila, Symmachus, and Theodotion.