Duration of Copyright
Anything you wrote after January 1, 1978, is protected from the date of creation to a date 70 years after your death. If you have a co-author, it is until 70 years following the death of the last surviving author. If you created the piece anonymously or wrote it under a pseudonym, the work is protect for 95 years after publication or 120 years after creation, whichever is shorter. If your material was written prior to January 1, 1978, the original copyright is extended to a maximum total of 95 years.
Note that the current copyright law does not restore copyright protection to any works already in the public domain. Going into public domain is what happens to a work that was never copyrighted (prior to 1978), or for which the copyright has already expired. Once in public domain, the public is free to quote from it without having to ask permission (although you do still give credit to the author). In essence, it then belongs to the public—not to the author. Most government publications are not copyrighted, so they are good sources for research that does not require you to ask permission.