Copyright and Public Domain

Cornell University online offers one of the most complete compilations of the confusing information about what works are in the public domain and how copyright works in Copyright Term and the Public Domain in the United States. It's way to large to reproduce here, although offered under a Creative Commons Some Rights Reserved license of Attribution-NonCommercial License 2.5, and too complex to simplify. According to the information provided:

This chart was first published in Peter B. Hirtle, "Recent Changes To The Copyright Law: Copyright Term Extension," Archival Outlook, January/February 1999. This version is current as of 1 January 2007. ...

The chart is based in part on the previously referenced Laura N. Gasaway's chart, "When Works Pass Into the Public Domain," at <http://www.unc.edu/~unclng/public-d.htm>, and similar charts found in Marie C. Malaro, A Legal Primer On Managing Museum Collections (Washington, D.C.: Smithsonian Institution Press, 1998): 155-156.

Be sure to read the footnotes to be fully informed. It's also available in a .PDF version.