Earlier this year, the New York Public Library (NYPL) announced preliminary results from an analysis of copyright registration and renewal data recorded with the U.S. Copyright Office from 1923-1964. The data reveals that of the approximately 642,000 copyrights registered for books during this period, the copyrights for approximately 162,000 (or 25%) of these books were renewed. This means that the roughly 480,000 books for which copyright was not renewed are most likely in the public domain (with a few caveats—for example, if the book was first published abroad).

The details of what, exactly, is in copyright from this period and for how long can be complicated, due to changes in copyright duration and renewal requirements during the 20th century. Shorter copyright terms, combined with a requirement to renew copyright in order to extend those terms, mean that many works published between 1923 and 1964 could have fallen out of copyright and into the public domain because their copyrights were not renewed. (On January 1, 2019, works from 1923 that were previously under copyright and renewed entered the public domain, marking the first time in 20 years that works have been added to the public domain in the United States due to term expiration.)

As the NYPL’s Sean Redmond points out, “For a long time, any book published before 1923 has surely been in the Public Domain and any book published after 1963 has positively been in copyright. Between those two dates though there is a more complex zone I’ll call the Renewal Era.” *

Identifying the copyright status of books in the so-called “Renewal Era” has taken a leap forward thanks to the pilot project undertaken at the NYPL to convert multiple volumes of the Library of Congress’ Catalog of Copyright Entries from scanned images to XML. This data, now searchable, consists of a list of books registered for copyright from 1923-1964 in the U.S., as well as list of those that had their copyright renewed during the same period. A search interface for the 1923-1964 registration and renewal records is available here.

Volunteers coordinated by Project Gutenberg and Internet Archive are now working to make these public domain books available online.

* It is also possible for works first published in the United States between January 1, 1964 and March 1, 1989 to have fallen into the public domain for failure to meet notice requirements. For more information, see Peter Hirtle’s Copyright Term and the Public Domain Chart or UC Berkeley Samuelson Law, Technology & Public Policy Clinic’s Public Domain Handbook.