The Lost Princess of Oz 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 Wizards 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 authors newborn granddaughter Ozma Baum, child of his youngest son Kenneth Gage Baum.