The Complete Wizard of Oz Collection

The Oz books form a book series that begins with
The Wonderful Wizard of Oz, and that relates the "history" of the Land of
Oz. Oz was originally created by author L. Frank Baum, who went on to write
fourteen Oz books. Although most of the Oz books are strictly adventures,
Baum—as well as many later Oz authors—styled themselves as "Royal Historians" of
Oz to emphasize that Oz is a genuine place. Later authors wrote 26 other
"official" books after Baum's death. Many other authors have put their own
twists on Oz, notably Gregory Maguire's revisionist Wicked. For more such
books, please see List of Published Oz Apocrypha.

— Excerpted from Wikipedia, the free encyclopedia.