Help:When does music enter the public domain?
In general, if a piece of music doesn't have a copyright notice on it, it might be in the public domain. But the rules and exceptions are very convoluted, so do not take these general guidelines as legal precedent in any way.
A piece of music enters into the public domain a certain amount of time after it's first written. But the time interval is different in each country.
CPDL is based in the U.S.A. Under U.S. copyright law, all music published before 1923 is now public domain (though new editions of these works may still be copyrighted), and much music which was not renewed since then is also in the public domain. Also, facsimiles of original older or out-of-copyright scores and older publications are not copyrightable.
Copyright law was changed in 1976. Before 1976, US Copyright Law stated that copyright existed for registered works for 28 years and could be renewed for an additional 28 years. After 1976, US Copyright Law states that for music published before 1976, the term of copyright is the original 28 years plus an additional 47 years (equals 75 years).
A new copyright law was subsequently passed which has extended the length of copyright for another 20 years. However, music in the public domain has not suddenly become copyrighted. If a piece was in the public domain, it remains in the public domain (with a few exceptions).
In Europe the general rule is that copyright protection exists until 70 years after the composer's death - though sometimes the copyright persists because it is owned by a publisher or by the composer's 'estate' rather than by the composer himself.
People downloading scores from CPDL should familiarize themselves with their local copyright laws. For example, a score may be on CPDL because the work has passed into the public domain in the U.S., but may still be in the public domain in other countries.
Users posting scores to CPDL additionally need to ensure that the score is not violating U.S. copyright laws, in addition to complying with the laws of their own country.
More information about copyright: About Copyright US Copyright Office Website Handy summary of Copyright law at Cornell University
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