Original works of authorship are protected by current copyright law for the life of the author, plus 70 years. For joint works, it is 70 years after the death of the last surviving author. If the work is anonymous, it is protected for 95 years after the first publication, or 120 years after its creation, whichever occurs first.
This has not always been the case. The English Statute of Anne in 1710 protected works for 14 years if published before 1710 and 21 years if published after. If the author survived until the end of the term, it was extended for another 14 years. The Statute of Anne influenced the American Copyright Act of 1790, which protected works for 14 years, with the possibility of another 14 if the author was still alive.
Lobbying and longer life spans contributed to extensions in copyright duration. It is possible copyright duration will be extended again in the future. This article provides an interesting perspective on copyright duration. It argues that current law provides too much protection, and harms the public. The purpose of copyright grants is to promote progress, which does not occur if the law provides too much protection. Copyrights are not simply a reward to the author. They are granted to spur innovation insofar as they do not harm the public.