I saw this paper and thought it might be useful for some E-Sylum readers who are trying to ascertain the copyright status of books. The paper's author is a recognized expert on copyright related to libraries and higher education, so while the paper is oriented for academics, this is going to be one of the more detailed and authoritative accounts out there.

In the course of many projects you might need to determine whether a particular book is in the public domain or is still protected by copyright. If protected, your ability to reproduce, digitize, or use the book in some other way will be defined by law or permission from the rightsholder. If the work is in the public domain, it is free of copyright limits and restrictions.

Almost all original writings are eligible for copyright protection, and copyrights last a long time. They do eventually expire—which places the work in the public domain. This paper is intended to guide you through the exercise of tracking the duration of copyright on a specific book of your choosing, and in process will tell when it may have entered or will enter the public domain. The process may not be as easy as it should, but online resources now make it much simpler. The effort can also produce important and useful results.

Another good source is this chart by another librarian copyright expert. copyright.cornell.edu/resources/publicdomain.cfm .