Copyright Term in The Public Domain in the United States

Here is a resource link to information concerning the Copyright Term for published and unpublished works.  The chart identifies copyright works which become part of the public domain.  A copyright is dependent on when the work was first published, whether or not the work was registered as a copyright and whether the publication was in the United States or abroad.  Note that song recordings have a separate chart, as do architectural works.

Copyright Term and the Public Domain in the United States