Jon, there really are two related issues here: How does digitalization impact in-copyright works and how long does copyright last?

One of things Google Books does is it allow users to access “snippets” (a few lines) of in-copyright works. The Supreme Court’s decision action effectively means that this practice can continue as a “fair use” under U.S. copyright law. The Atlantic provides a nice summary of the underlying Second Circuit decision here.

Sometimes you want access to a whole text and not just a snippet, and Google Books provides that too for out-of-copyright works. As a World War I naval historian, Google Books and even more so the Hathi Trust, a partnership between Google and leading university research library, makes what I do much, much easier. There are lots of very important works such as Lloyd’s Register of Shipping, The Record of American and Foreign Shipping, the Rangliste der Kaiserlich Deutschen Marine (list of German naval officers for a particular year), Rang- und Einteilungsliste der k. u. k. Kriegsmarine (list of Austrian naval officers for a particular year) from that period that I can now easy access from the comfort of my home for free.

There’s just one limitation: Such books have to be published in 1922 or earlier. Under the 1998 Copyright Term Extension Act, Congress extended the period of copyright protection for works published in 1923 and later to 95 years while leaving works published in 1922 and earlier in the public domain (the previous 75-year period for a work published in 1922 expired at the beginning of 1998). This means that on January 1, 2019 for the first time in 21 years some works’ copyrights are set to expire and enter the public domain. That is, of course, unless Congress decides to extend copyright protection again… which is something that Disney and other media corporations will almost certainly strongly lobby for.