is the eleventh canonical Oz book written by L. Frank Baum. Published on June 5, 1917, it begins with the disappearance of Princess Ozma, the ruler of Oz and covers Dorothy and the Wizard's efforts to find her. The introduction to the book states that its inspiration was a letter a little girl had written to Baum: "I suppose if Ozma ever got hurt or losted, everybody would be sorry."
The book was dedicated to the author's newborn granddaughter Ozma Baum, child of his youngest son Kenneth Gage Baum.
Ruth Plumly Thompson borrowed the plot of this novel for her 1937 Oz book Handy Mandy in Oz. The Frogman and Cayke's dishpan re-appear in Jeff Freedman's 1994 novel The Magic Dishpan of Oz.