You don't need to visit a bookstore or even an online retailer to find new reading material. Millions of books published decades ago are now in the public domain—and the New York Public Library is making it easier than ever to find these titles and download them for free. According to Vice, many books published before 1964 whose copyright status was previously unknown have been revealed by the library to be in the public domain.

Today, new books generally hold their copyright for 70 years following the author's death, but a few decades ago, the law worked differently. Any books published before 1964 had a copyright term of 28 years, and authors or publishers had to fill out separate paperwork if they wanted to extend it. Most either forgot or chose not to, and today roughly 80 percent of books published in the U.S. between 1923 to 1964 are in the public domain.

In the 1970s, the Library of Congress maintained a catalog of which books had their copyrights renewed, and anyone can view digital copies of that information on the Internet Archive. A quick glance at the documents makes it clear that many new books have entered the public domain recently—but tallying all of them posed a problem. The data was too vast for computers to process, preventing many repositories from determining which books were legal to upload.

The New York Public Library tackled this issued by converting the Library of Congress's catalog into an XML format. Thanks to the library's ambitious project, the copyright status of all American books published between 1923 and 1964 is searchable, and public domain websites are now busy updating their archives.

If you're interested in browsing the new titles that are now free and legal to read and download, there are multiple online databases worth checking out. Project Gutenberg, the Hathi Trust, and the Internet Archive are great places to find both old and recent entries to the public domain.

[h/t Vice]