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..
L. Frank Baum
In 1900, Baum and Denslow (with whom he shared the copyright) published "The Wonderful Wizard of Oz" to much critical acclaim and financial success. The book was the best-selling children's book for two years after its initial publication. Baum went on to write thirteen more novels based on the places and people of the Land of Oz.