Evolving international norms thus explain the most significant change in US copyright term: the shift to the method for calculating the postmortem-author component of copyright term prescribed by the Berne Convention for the Protection of Literary and Artistic Works, which the US first adopted in the Copyright Act of 1976 and reaffirmed in the Copyright Term Extension Act of 1998
That deadline was set by the Sonny Bono Copyright Term Extension Act of 1998
, which retroactively increased the copyright terms of pre-existing as well as new works.
The following sections discusses the Berne Convention, the WIPO (World Intellectual Property Organization) Copyright Treaty Act, the DMCA (Digital Millennium Copyright Act), the TEACH (Technology, Education, and Copyright Harmonization) Act, and the Sonny Bono Copyright Term Extension Act of 1998
. The final section addresses public domain.
The DMCA and the Sonny Bono Copyright Term Extension Act of 1998
(known as the "Sonny Bono Law")  change the law in matters of potentially great significance to libraries.
Then the Copyright Term Extension Act of 1998
added another 20 years of protection.