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 story chronicles the adventures of a young farm girl named Dorothy in the magical Land of Oz, after she and her pet dog Toto are swept away from their Kansas home by a cyclone. The novel is one of the best-known stories in American literature and has been widely translated. The Library of Congress has declared it "America's greatest and best-loved homegrown fairytale." Its groundbreaking success and the success of the Broadway musical adapted from the novel led Baum to write thirteen additional Oz books that serve as official sequels to the first story.