The copyright status of The Wizard of Oz and related works is complicated for several reasons. The book series is very long-running, and written by multiple authors, so the books often fall on opposite sides of eligibility for copyright laws. There have also been multiple adaptations across many different media, which enjoy different kinds of copyright protection. The copyright law of the United States has changed many times, and impacted Oz works every time. As of 2021, twenty-six Oz books and five movies are in the public domain. Starting in 2019, an Oz book has entered the public domain every year. Barring another extension of copyright terms, all of the Famous Forty will be in the public domain by 2059.