Copyright status of The Wizard of Oz and related works in the United States
"The Wonderful Wizard of Oz" was published in 1900, and was the first to enter the public domain in "1956". This allowed Reilly & Lee, the publisher of all the other Oz books (as well as Baum's other books) to issue their own edition of "The Wizard of Oz", which had previously been published by George M. Hill Company and later by the Bobbs Merill Company after Hill went bankrupt..
The Wonderful Wizard of Oz
The Wonderful Wizard of Oz () is an American children's novel written by author L. Frank Baum and illustrated by W. W. Denslow, originally published by the George M. Hill Company in Chicago on May 17, 1900. It has since seen several reprints, most often under the title The Wizard of Oz, which is the title of the popular 1902 Broadway musical adaptation as well as the iconic 1939 musical film adaptation.