The musical is based on Gregory Maguire's bestselling 1995 novel, Wicked: The Life and Times of the Wicked Witch of the West, and serves as a prologue to Lyman Frank Baum's 1900 classic The Wonderful Wizard of Oz (as well as its movie equivalent, MGM's 1939 The Wizard of Oz). It explains what happened before Dorothy Gale arrived in the Land of Oz. The musical version of Wicked ignores the sequels to Maguire's other Wicked books, Son of a Witch (published in 2005), A Lion Among Men (published in 2008), and Out of Oz (published in 2011).