Glenn Fleishman, writing for Smithsonian Magazine:

At midnight on New Year’s Eve, all works first published in the United States in 1923 will enter the public domain. It has been 21 years since the last mass expiration of copyright in the U.S.

And:

“The public domain has been frozen in time for 20 years, and we’re reaching the 20-year thaw,” says Jennifer Jenkins, director of Duke Law School’s Center for the Study of the Public Domain. The release is unprecedented, and its impact on culture and creativity could be huge. We have never seen such a mass entry into the public domain in the digital age. The last one—in 1998, when 1922 slipped its copyright bond—predated Google. “We have shortchanged a generation,” said Brewster Kahle, founder of the Internet Archive. “The 20th century is largely missing from the internet.”

And:

We can blame Mickey Mouse for the long wait. In 1998, Disney was one of the loudest in a choir of corporate voices advocating for longer copyright protections. At the time, all works published before January 1, 1978, were entitled to copyright protection for 75 years; all author’s works published on or after that date were under copyright for the lifetime of the creator, plus 50 years.

Fascinating read.