The Septuagint [LXX] was the first translation of the Hebrew Bible and was made in the third century B.C. by Jewish scribes, who were direct descendents of those trained in Ezra's Great Synagogue of Jerusalem. They were complete experts in the text, being very well versed in Hebrew and Greek.
This translation became very popular among Jews in the first two centuries before Christ because many Jews in those days did not understand Hebrew. Their ancestors had left Israel centuries before, and generation after generation gradually lost the ability to read the Scriptures in Hebrew.
Many of the Jews in Jesus' day used the Septuagint as their Bible. Quite naturally, the early Christians also used the Septuagint in their meetings and for personal reading; and many of the New Testament apostles quoted it when they wrote the Gospels and Epistles in Greek. What is most fascinating is that the order of the books in the Septuagint is the same order in our Bibles today, and not like the Hebrew scrolls....
Jesus and the Apostles studied, memorized, used, quoted, and read most often from the Bible of their day, the Septuagint. Since Matthew wrote primarily to convince the Jews that Jesus of Nazareth was indeed their promised Messiah, it follows as a matter of course that his Gospel is saturated with the Hebrew Scriptures. Yet, when Jesus quotes the Old Testament in Matthew, He uses the Hebrew text only 10% of the time, but the Greek LXX translation 90% of the time!
Amazingly, Jesus and Paul used the LXX as their primary Bible. It was just like the Bible each of us holds in our hands, not the original Hebrew Old Testament, but a translation of the Hebrew into Greek. But it was based on exactly the same original and inspired words, and reads just like the Bible we hold in our hands today.
Taken from "What Bible Did Jesus Use?" by Discover the Book Ministries (used by permission).