The Septuagint is the most ancient translation of the Old Testament which is, today, the official text of the Orthodox Church.

The Septuagint (meaning "of the Seventy") was accepted by the Jews of Alexandria and then by all Greek-speaking countries. This text laid the groundwork for the spread of the Gospel among the Jews outside Palestine and among the Gentiles as well. This version is first mentioned in Aristeas' letter to his brother, Philocrates. The King of Egypt, Ptolemy II Philadelphus, built a beautiful library at Alexandria and decided to include among its texts a copy of the Jewish scriptures.

The king asked the Jewish high-priest, Eleazar, in Jerusalem (who had the title and style of king as well) to send him a copy of the Law and a group of translators.

Seventy-two Israelites, six from each of the 12 tribes, were sent to Egypt by the high-priest for this purpose. According to tradition, these 72 worked on a Greek translation of the Old Testament and their labour lasted for 72 days. The translation was read out loud before the Jewish priests, princes and people at Alexandria and it was given unanimous approval as a translation that was in perfect conformity with the Hebrew original and this was placed in the library.

The 72 scribes translated not only the five books of Moses, but the entire Old Testament accepted by the Orthodox Church today, including the Book of Psalms that is used most copiously in the liturgy and services of the Orthodox Church. There are later critical reviews of this tradition, but this is the view of the Church.

The number "72" figures prominently and reflects the number of judges that Moses chose to assist him in his administration over the 12 tribes of Israel.

Christ Himself likewise appointed the same number of Disciples who assisted the 12 Apostles in preaching the Gospel.

Here is a very good site on the study of the Septuagint:

http://arts-sciences.cua.edu/ecs/jdk/LXX/