May I apply a Creative Commons license to a work in the public domain?

Answer:

CC licenses should not be applied to works in the worldwide public domain. All CC licenses are clear that they do not have the effect of placing restrictions on material that would otherwise be unrestricted, and you cannot remove a work from the public domain by applying a CC license to it. If you want to dedicate your own work to the public domain before the expiration of applicable copyright or similar rights, use CC’s legally robust public domain dedication. If a work is already in the worldwide public domain, you should mark it with CC’s Public Domain Mark.

Note that, in some cases, a work may be in the public domain under the copyright laws of some jurisdictions but not others. For example, U.S. government works are in the public domain under the copyright law of the United States, but may be protected by copyright laws in other jurisdictions. A CC license applied to such a work would be effective (and the license restrictions enforceable) in jurisdictions where copyright protection exists, but would not be operative if U.S. copyright law is determined to be the applicable law.

Creators may also apply Creative Commons licenses to material they create that are adapted from public domain works, or to remixed material, databases, or collections that include work in the public domain. However, in each of these instances, the license does not affect parts of the work that are unrestricted by copyright or similar rights. We strongly encourage you to mark the public domain material, so that others know they are also free to use this material without legal restriction.