"CPDL stands for 'Choral Public Domain Library', an internet-based free sheet music website which specializes in choral music."
Over 7,500 works from over 1,200 composers.
"The CPDL copyright license applies to all scores and texts which reside on the CPDL server. This is a type of open-source license which allows users to download, print, copy and distribute a score freely. The only restriction is that, if any changes are made to a score or text, the subsequent modified version must still be released under the same license conditions. The license is based on the GNU GPL License, which is very common in software development."