Copyright

If a work is in the public domain, that means you do not need any permissions or copyright exceptions to use it freely.  Works in the public domain include:

• The copyright term has expired
• Works so old they were never under copyright
• Copyright was improperly renewed 
• The author has waived all copyright restrictions
• Publication by a government agency
• Laws that have been enacted by a local, state, or federal government 
• Works not subject to copyright or other intellectual property protections (patent, trademark). For example, ideas themselves cannot be copyrighted, just their expression on a page.

If it meets one of the following criteria, it is most likely in the public domain:

• Works published in or before 1923
• Works published prior to 1964 where copyright was not renewed (renewal was a requirement until 1978)
• Works published prior to March 1, 1989 that do not include a proper copyright notice (the (c) symbol)
• Facts or ideas (although the specific way these facts or ideas are written down is subject to copyright)

If you're ever unsure, ask a librarian for help!