What is public domain?
Copyright protection does not last forever. Once copyright expires, a work may be used without permission. Congress has repeatedly, however, lengthened the period for which a work is eligible for copyright protection. The most recent legislation was the Copyright Term Extension Act, also known as the Sonny Bono Copyright Term Extension Act. This bill passed in 1998 and extended the copyright term for most protected works to the life of the author plus 70 years. Be warned that the passing of an original edition of a work into the public domain does not mean that later editions or translations are not protected.