It's a companion to the 12-book fantasy series comprised of the The Belgariad, The Malloreon, Belgarath the Sorcerer and Polgara the Sourceress. In David Edding's words, The Rivan Codex "may give the student of our genre some insights into the creative process--something of the order of 'connect wire A to wire B'. This is a collection of the groudwork the authors laid for the Belgariad and Malloreon series.