A short 3.5-page intro to the Septuagint by Emanuel Tov
Emanuel Tov is J. L. Magnes Professor of Bible at Hebrew University in Jerusalem. Among many other publications, his Textual Criticism of the Hebrew Bible contains a wealth of information for the student of the Septuagint and Hebrew Bible.
On his site there are lots of pdf articles you can read for free. One particularly helpful one is this very short introduction (3.5 pages) to the Septuagint. It covers the name of the Septuagint, its nature and content, date, origin, background, and more.