One of the most frequent questions asked by writers (and bloggers) is whether a particular work they wish to quote at length (potentially beyond the bounds of fair use) -- or even republish in its entirety -- is still protected by copyright. It can be a more complicated question than one might expect.
One short answer is that, if a work was first published in 1922 or before, the copyright in the United States has expired, and the work is in the public domain in the United States. However, you must be careful to quote from the work as it existed in 1922 or before. Later editions of the work could contain new or different copyrightable expression first published after 1922, and that expression could still be copyright protected. (There is also a bit of disagreement among courts as to when the copyright term begins if the work was first published outside of the United States without a United-States-style copyright notice, but we will skip over that subtlety here.)
Matters are further complicated by the fact that copyright is territorial. The duration of copyright in other countries is computed differently, a subject I will return to in later posts. As a result, even though the copyright in a work has expired in the United States, it could still be copyright-protected in other nations.
Further complications arise from the fact that many post-1922 works that once enjoyed copyright in the United States have lost their copyright protection over the years by reason of the failure to register and renew the copyrights or to comply with other statutory formalities, particularly the formalities of the old 1909 Copyright Act. Additionally, works created prior to January 1, 1978, that were unpublished as of that date, have their own complicated set of rules concerning copyright duration.
The best short summary of the duration of U.S. copyright is to be found here on the Cornell website. It is based in part on Laura Gassaway's simpler chart found here.