It is the earliest extant Greek translation of the Old Testament from the original Hebrew. One should not confuse the Septuagint with other Greek versions of the Old Testament, most of which did not survive except as fragments. Modern critical editions of the Septuagint are based on the Codices Vaticanus, Sinaiticus, and Alexandrinus. The Septuagint seems to have been a major source for the Apostles, but it is not the only one.