Merry Go Round in Oz is the last of the "Famous Forty" and the last "official" Oz book. Reilly & Lee had refused many other authors, including previous author Rachel R. Cosgrove, to publish a fortieth Oz book because of poor sales, but were persuaded by McGraw's two Newbery Awards to admit a fortieth book into the series. The first edition, the so-called "white edition," is the rarest book in the series in its original printings.