Commons:Multi-licensing

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This page in a nutshell: Multi-licensing means releasing content under multiple licenses. Doing so gives more freedom to users of the content, as they can choose which of the licenses best suits their needs.

Multi-licensing means releasing content under multiple licenses. Doing so gives more freedom to users of the content, as they can choose which of the licenses best suits their needs. Multi-licensing with restrictive licenses may be desirable for compatibility with the licensing scheme of other projects; also, multi-licensing allows people who create derivative work to release that work under a restrictive license only, if they wish—that is, it gives creators of derivative works more freedom with regards to which license they may use for their work.

Multi-licensing on Commons

Many Commons users choose to dual-license their works under the GFDL and the CC-BY-SA license (all versions), using the copyright tags {{GFDL}} and {{Cc-by-sa-all}}. Both licenses have a ShareAlike restriction, ensuring the work will remain free no matter how it is used or modified. Using 'all versions' of the CC-BY-SA license maximises re-usability for sites which may be "stuck" with an earlier version of the CC-BY-SA license.

Contributors to Wikimedia Commons can offer as many licenses for a file as they wish, as long as at least one of them meets the criteria for free licenses specified in the licensing policy. For example, files under a "non-commercial" license are OK only if they are at the same time also released under a free license that allows commercial use.

Copyright holders can release a file under additional licenses at any time, but cannot revoke licenses (Commons does not permit licenses which can be revoked - see License revocation). Commons tries to preserve mention on the file's file description page of all licenses that a file has been released under, as this can provide flexibility for re-users, and helps re-users show that they are respecting the relevant copyright.

Example

Example: how multi-licensing under both {{Cc-by-sa-all}} (CC-BY-SA) and {{Cc-by-nc-sa-2.0-dual}} (CC-BY-NC-SA) can allow several images to be combined in a collage that otherwise could not be:

Licence (image 1, from Commons)	Licence (image 2, from another source)	Permissible licenses for collage	Explanation
CC-BY-SA	CC-BY-NC-SA	No license is permissible	The collage must be published under a licence which allows commercial usage (CC-BY-SA) while at the same time it must be published under a licence which forbids commercial usage (CC-BY-NC-SA). The collage is necessarily a copyright violation, since it can't satisfy both licenses at once.
CC-BY-SA CC-BY-NC-SA	CC-BY-NC-SA	CC-BY-NC-SA is permissible	Image 2 requires a non-commercial licence (CC-BY-NC-SA) while image 1 allows both commercial and non-commercial licences. The collage creator must apply CC-BY-NC-SA.
CC-BY-SA	CC-BY-SA CC-BY-NC-SA	CC-BY-SA is permissible	Image 1 requires a commercial licence (CC-BY-SA) while image 2 allows both commercial and non-commercial licences. The collage creator must apply CC-BY-SA.
CC-BY-SA CC-BY-NC-SA	CC-BY-SA CC-BY-NC-SA	CC-BY-SA or CC-BY-NC-SA (or both) is permissible	Both images allow both commercial and non-commercial licences - the collage creator can choose which to apply, or apply both.
CC-BY-SA-2.0	CC-BY-SA-3.0	CC-BY-SA-3.0 is permissible	If different versions of the same Attribution-ShareAlike license are used for different images, the newer one must be used for any collage made from them.
CC-BY-SA-1.0	CC-BY-SA-3.0	No license is permissible	Version 1.0 of the Attribution-ShareAlike license is not compatible with later versions.

This shows how dual-licensing CC-BY-SA+CC-BY-NC-SA gives more freedom than just CC-BY-SA, as well as various consequences of having different versions of CC licenses.

Wikimedia multi-licensing (2009 GFDL license migration)

See Wikipedia:Image license migration.