January 1st is Public Domain Day, and that means that under the current copyright law, the works of artists, writers, and musicians who died 70 years ago (1941) become freely available to copy, adapt, translate, and otherwise use. This year marks the entrance of works from some famous authors, including James Joyce and Virginia Woolf, but there could have been more. The maximum length of a copyright used to be 56 years, meaning Disney's Lady and the Tramp, J.R.R. Tolkien's Return of the King, and Alfred Hitchcock's To Catch a Thief (all released in 1955) would have entered the public domain today. But in 1976, copyrights were extended for the life of the author plus 50 years or 75 years on works made for hire, and a 1998 amendment further extended those terms to 70 years and 95 years respectively. If not for the latter change, Ernest Hemingway's works, Charlie Chaplin's Modern Times, and the first issue of Life magazine would be entering the public domain today.
Protecting works from Tolkien and Hitchcock is one thing because they're still commercially viable, but there's a large number of "orphan works" that don't have clear copyright owners and are still under protection. The risk of getting sued for using them, and the effort of finding someone who can license the rights are often enough to deter most uses. Until that problem is solved, you can celebrate the works that are definitely in the clear at Public Domain Day, or pout over what could have been at Duke Law.
Update: This post was edited to better reflect legal history