License

Backdrop is GPL version 2 (or later) software. Distributions of Backdrop may relicense it as any later version of the GPL.

Copyright

All Backdrop code is copyright by the original authors.

Backdrop includes works under other copyright notices and distributed according to the terms of the GNU General Public License or a compatible license. Individual works may have specific copyright information noted within their their source code files or directories.

FAQ

If I write a module or theme, do I have to license it under the GPL?

Yes. Backdrop modules and themes are a derivative work of Backdrop. If you distribute them, you must do so under the terms of the GPL version 2 or later. You are not required to distribute them at all, however. (See the next question below.)

When distributing your own module or theme, therefore, the GPL applies to any pieces that directly interact with parts of Backdrop that are under the GPL. Images and Flash files you create yourself are not affected. However, if you make a new image based off of an image that is provided by Backdrop under the GPL, then that image must also be under the GPL.

If I write a module or theme, do I have to give it away to everyone?

No. The GPL requires that if you make a derivative work of Backdrop and distribute it to someone else, you must provide that person with the source code under the terms of the GPL so that they may modify and redistribute it under the terms of the GPL as well. However, you are under no obligation to distribute the code to anyone else. If you use the code only personally or only within your organization, then the code is not distributed, so the requirement of providing the source code does not apply.

However, if your module is of general use then it is often a good idea to contribute it back to the community anyway in a public repository. You can get feedback, bug reports, and new feature pull requests from others who find it useful.

Is it permitted for me to sell Backdrop or a Backdrop module or a Backdrop theme?

Yes. However, you must distribute it under the GPL version 2 or later, so those you sell it to must be allowed to modify and redistribute it as well (potentially at no cost). See the previous question.

Can I release my work under GPL version 3 or under GPL version 2-only?
Yes. Because users of Backdrop may choose which version of the GPL license they wish to use (version 2 or version 3), any module or theme written for Backdrop may be distributed under either license exclusively. However, if the module is packaged together with Backdrop, all the code included in the package must be under the same license. For that reason, any module or theme that integrates with Backdrop is encouraged to use the same "GPL version 2 or higher" license.

Will Backdrop move to GPL version 3?

Because Backdrop is licensed under the GPL version 2 or later, Backdrop may be distributed under GPL version 3. This provides the flexibility to users to choose their own license version. At this time, there are no plans to begin distributing Backdrop under only version 3 or later.

Portions of this page were modified from the Drupal.org Licensing FAQ