After Alexander the Great conquered most of the Middle Eastern world, the area became heavily influenced by Greek culture and language (what historians refer to as Hellenization). Most Jews outside of Palestine (and most people for that matter) spoke Greek by the 3rd Century BC. As a result, the Jewish leadership convened a meeting of 70 Jewish scribes in circa 250BC to translate the Scriptures into Greek. This took place in Alexandria, Egypt. This Greek translation of the Old Testament became known as the Septuagint – named as such, for the 70 translators who transcribed it. It is also designated by the Roman numerals ‘LXX’.
We have copies of the LXX dating back as far as 150BC.
LXX divides one of the Psalms so that there are 151 in total.
LXX reorders the 6th and the 8th Commandments exchanging Exodus 20: 13 with Exodus 20: 15
The words of Cain in Genesis 4: 8 appear to be left out of the Masoretic text
As with the Samaritan Pentateuch, there are a few age discrepancies in Genesis 5 and Genesis 11 when you compare it to the Masoretic Text