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. Currently, twenty-three Oz books and one movie are in the public domain. Nothing else will enter the public domain until 2019 at the earliest. All of the Famous Forty will be in the public domain in 2059, barring another extension of copyright terms.