What is public domain?
Public domain is a work that is no longer under copyright protection. Works in public domain may be used freely without the permission of the former copyright owner (US, Copyright Office, 2013)
All work is in public domain when it meets this criteria:
Work created after 1977 does not fall into public domain until 70 years after the death of the author. For corporate works it is 95 years from publication date or 120 years from creation date.
Work created since 1989 are presumptively protected by copyright.
What resources are in public domain?
Use this handy tool to determine if the resource you want to use is protected by copyright? Use the Digital Copyright Slider from ALA's Office for Information Technology Policy.