Duration of Copyright: Public Domain

A work in the public domain is one that can be freely used by anyone for any purpose.  A work in public domain is not protected by copyright.  Public domain is the realm embracing property rights that belong to the community at large, are unprotected by copyright or patent, and are subject to appropriation by anyone.  It is important to know when works are protected by copyright and when they are not, or are in the "public domain."  These resources can help:

When works pass into the public domain (A chart prepared by University of North Carolina law library director Laura Gasaway)

How to Investigate the Copyright Status of a Work (Circular 22 from the US Copyright Office)

Copyright Search (The U.S. Copyright Office's new Web-based copyright search for information about millions of books, music recordings, movies, software and other works. Includes copyright records dating back to 1978 in three categories: General Works, consisting of books, music, films, maps, and software; Serials, such as magazines and newspapers; and Documents, such as contracts, licenses, and wills that relate to copyright ownership)

How Long Copyright Protection Endures (from Circular 1 from the US Copyright Office)