Each outline features the major divisions of the book, plus the period of Old Testament history in which it occurs. Go here for a quick review of those periods.
Some of these outlines are original, some are adapted, and some are from one of three sources I used:
David Dorsey. The Literary Structure of the Old Testament. (Grand Rapids, Mich.: Baker, 1999).
R. K. Harrison. Introduction to the Old Testament. (Grand Rapids, Mich.: Eerdmans, 1969).
Harold Lindsell. Harper Study Bible. (Grand Rapids, Mich.: Zondervan, 1965).