The book was published by George M. Hill Company. The first edition had a printing of 10,000 copies and was sold in advance of the publication date of September 1, 1900. On May 17, 1900, the first copy came off the press; Baum assembled it by hand and presented it to his sister, Mary Louise Baum Brewster. The public saw it for the first time at a book fair at the Palmer House in Chicago, July 5–20. Its copyright was registered on August 1; full distribution followed in September. By October 1900, it had already sold out and the second edition of 15,000 copies was nearly depleted.
In a letter to his brother, Harry, Baum wrote that the book's publisher, George M. Hill, predicted a sale of about 250,000 copies. In spite of this favorable conjecture, Hill did not initially predict that the book would be phenomenally successful. He agreed to publish the book only when the manager of the Chicago Grand Opera House, Fred R. Hamlin, committed to making it into a musical stage play to publicize the novel. The play The Wizard of Oz debuted on June 16, 1902. It was revised to suit adult preferences and was crafted as a "musical extravaganza," with the costumes modeled after Denslow's drawings. Hill's publishing company became bankrupt in 1901, so Baum and Denslow agreed to have the Indianapolis-based Bobbs-Merrill Company resume publishing the novel.
Baum's son, Harry Neal, told the Chicago Tribune in 1944 that Baum told his children "whimsical stories before they became material for his books." Harry called his father the "swellest man I knew," a man who was able to give a decent reason as to why black birds cooked in a pie could afterwards get out and sing.
By 1938, more than one million copies of the book had been printed. By 1956, the sales of it had grown to three million copies in print.