Wikipedia:Revocation of our licensing is not permitted

Contributions to Wikipedia are licensed under free content licenses, such as the GNU Free Documentation License (GFDL) and the Creative Commons Attribution Share-Alike license. It is not legally possible for individuals or organizations who contribute to Wikipedia to revoke these licenses, as this would affect the ability of the entire project to exist as a freely-editable, freely-available, encyclopedia, and the licenses themselves are specifically worded to not allow such a situation unless in certain circumstances.

Claims of this nature present a serious risk to the site because they are proclaiming an intention not to abide by the licensing agreement that makes the entire site possible. Wikipedia is not possible without free content licenses, which allows our content to be freely distributed and freely edited. Editors must be aware that they do not have a right to challenge the entire basis of the project and continue participating in it at the same time.

The Wikimedia Foundation, which runs the English Wikipedia and various other projects, has not expressed an opinion on this matter.

The inability to revoke
The messages below the edit box include the warning that "[contributors] irrevocably agree to release [their] contributions under the CC-BY-SA 3.0 license and the GFDL." The GFDL, Wikipedia's original license, is irrevocable, and can only be terminated under the provisions of Section 9 of the license, which allows an author to revoke the license from someone who has broken the conditions of the license. The Creative Commons Attribution Share-Alike license includes similar elements, including the statement that "[the] Licensor hereby grants [the user] a worldwide, royalty-free, non-exclusive, perpetual (for the duration of the applicable copyright) license to exercise the rights in the Work [...]", and a similar exit clause to the GFDL, which automatically revokes the license from users who have broken the conditions of the license.

Community-imposed sanctions
Editors in the past who have persisted in trying to revoke the GFDL terms of their work have been banned while they have persisted in their claim.

Making such a claim is akin to making legal threats. GFDL is not a Wikipedia community-generated policy. It is not subject to actionable community discussion or editing, nor is its applicability subject to debate outside of a court of law. In common with the way that editors are blocked while they threaten to pursue other kinds of legal action, someone who intends to mount a legal challenge against Wikipedia's use of the GFDL is not invited to edit Wikipedia while they do so.

Rights
All editors have the 'right to leave' and the 'right to fork'. However, this does not mean that their contributed content leaves with them; only their participation in the community ends, and all forked content is still subjected to the license terms of Wikipedia. They are, of course, able to license their own original contributions to a different site under different terms if they so choose.

Multi-licensing
Some editors have released their contributions under additional licenses by saying so on their user page. It is a subject of debate whether it is practically possible to reuse content from Wikipedia under the terms of an additional license. However, all original text contributions are still subject to the stated licenses of Wikipedia, regardless of any other additional licenses that an editor might apply to their contributions.

Termination rights
Under 17 USC 203 (A section of the US copyright law) any copyright owner has the right to terminate copyright grants (transfers or licenses) under certain circumstances. "(section 203(a)(1)): In the case of a grant executed by one author, termination of the grant may be effected by that author or, if the author is dead, by the person or persons who, under clause (2) of this subsection, own and are entitled to exercise a total of more than one-half of that author’s termination interest." "(section 203(a)(3)): Termination of the grant may be effected at any time during a period of five years beginning at the end of thirty-five years from the date of execution of the grant; or, if the grant covers the right of publication of the work, the period begins at the end of thirty-five years from the date of publication of the work under the grant or at the end of forty years from the date of execution of the grant, whichever term ends earlier." "(section 203(b)(3)): A further grant, or agreement to make a further grant, of any right covered by a terminated grant is valid only if it is made after the effective date of the termination. As an exception, however, an agreement for such a further grant may be made between the persons provided by clause (3) of this subsection and the original grantee or such grantee’s successor in title, after the notice of termination has been served as provided by clause (4) of subsection (a)." Termination requires at least two and up to ten years notice. Termination rights cannot be waived by any contract or license, so no copyright license can accurately claim to be (or be described as) irrevocable under US law.

There is no known instance of anyone who has licensed a work using a Creative Commons or GFDL license, or other open permissive license, invoking this provision.