This article is from the Piano General Topics FAQ, by Isako Hoshino firstname.lastname@example.org with numerous contributions by others.
Title 17, U.S. Code provides copyright protection for both
published and unpublished works, granting the owner of the
copyright exclusive rights over reproduction, creation of
derivative works, distribution of copies for sale or rent,
and public performance and display.
Copyright protects "original works of authorship" that are
"fixed in a tangible form of expression," such as scores or
sound recordings of musical works. Works that have not been
"fixed in a tangible form of expression," such as
improvisational performances that have not been written or
recorded, are not protected by copyright. Works for which
the copyright has expired are no longer protected; they are
in the public domain and cannot again receive copyright
Currently copyright is automatically secured upon the
creation of a work (as "fixed in a tangible form...");
publication or registration with the Copyright Office is not
required. Before 1978, copyright was generally secured by
means of publication with a copyright notice (e.g. Copyright
MCMXX by John Doe) or, for unpublished works, registration
with the Copyright Office. After March 1, 1989 the copyright
notice was no longer mandatory on copyrighted works.