All books published in the U.S. before 1924 are in the public domain, meaning they’re publicly owned and can be freely used and copied.
Per the Sonny Bono Copyright Term Extension Act of 1998, “corporate” creations (like Mickey Mouse) can be restricted under copyright law for 120 years. Per an amendment to the act, works published between 1923 and 1977 can enter the public domain 95 years after their creation, meaning that 2019 was the first year since 1998 that a large number of works entered the public domain.
It's estimated that up to 75 percent of books published between 1923 to 1964 are secretly in the public domain because most of their copyrights were never extended, making them free to read and copy today.
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