Works which are no longer covered under copyright protection or whose authors/copyright holders have waived their rights are considered works "in the public domain." This means they may be copied, performed, recorded, or otherwise distributed to the public--for profit or non-profit--without further permission. Eventually, all works will fall into the public domain because copyright is not eternal. (Note: See also this file on the Sonny Bono copyright extension act.)
Please note, however, that sometimes -editions- of public domain pieces are copyrighted. These receive the same treatement as any other piece of copyrighted music. (If you make an arrangement of a Beethoven sonata, your arrangement is protected by copyright.)
If the Copyright Office has no information that the author is still alive and it has been 75 years since copyright protection was first granted or 100 years since the creation of the piece, the piece falls into the public domain. Copyright protection has expired, and the author is presumed dead. So, anything copyrighted in 1922 is public domain (provided the author is presumed dead by the Copyright Office).
copyright 1996-2007, Martha Beth Lewis, Ph.D.