Materials in the public domain are not protected by copyright and may be freely used in their entirety.
Most federal government publications and works created prior to 1923 are in the public domain. Works created between 1924 and 1989 may be in the public domain, but require more investigation.
Which government documents are in the public domain?
The majority of documents published by the federal government are in the public domain. There are some exceptions. The federal government outsources some of its research and publications to private publishers. Those works may be copyrighted. Check the specific document.
Also many state and county publications may be copyrighted; they are not necessarily in the public domain.
How do I know if a work after 1923 is in the public domain?
This depends on whether the work was published, was registered, and whether the original copyright was renewed. Use these resources to check the status of the work in question:
A work can also be an "orphan work" meaning that it may still be under copyright, yet no rightsholder can be found.
For those who wish to explore further, see:
Nothing on this guide is to be construed as legal advice. These pages are intended to provide information and guidance in the application of copyright law and to expand on the University of Missouri System Collected Rules and Regulations.
Thanks to Miller Nichols Library of UMKC for permission to reuse material from their Copyright guide.