Licenses

Published software should be free software. To make it free software, you need to release it under a free software license. We normally use the GNU General Public License (GNU GPL), specifying version 3 or any later version, but occasionally we use other free software licenses. We use only licenses that are compatible with the GNU GPL for GNU software.

Documentation for free software should be free documentation, so that people can redistribute it and improve it along with the software it describes. To make it free documentation, you need to release it under a free documentation license. We normally use the GNU Free Documentation License (GNU FDL), but occasionally we use other free documentation licenses.

If you've started a new project and you're not sure what license to use, “How to choose a license for your own work” details our recommendations in an easy-to-follow guide. If you just want a quick list reference, we have a page that names our recommended copyleft licenses.

We also have a page that discusses the BSD License Problem.

Evaluating Licenses

If you come across a license not mentioned in our license list, you can ask us to evaluate whether it is a free license. Please email a copy of the license (and the URL where you found it) to licensing@fsf.org. Our licensing experts in the staff and the board of directors will review it. If the license has some unusual conditions, they may pose difficult philosophical problems, so we can't promise to decide quickly.

Common Resources for our Software Licenses

We have a number of resources to help people understand and use our various licenses:

The GNU General Public License

The GNU General Public License is often called the GNU GPL for short; it is used by most GNU programs, and by more than half of all free software packages. The latest version is version 3.

The GNU Lesser General Public License

The GNU Lesser General Public License is used by a few (not by any means all) GNU libraries. The latest version is version 3.

The GNU Affero General Public License

The GNU Affero General Public License is based on the GNU GPL, but has an additional term to allow users who interact with the licensed software over a network to receive the source for that program. We recommend that people consider using the GNU AGPL for any software which will commonly be run over a network. The latest version is version 3.

The GNU Free Documentation License

The GNU Free Documentation License is a form of copyleft intended for use on a manual, textbook or other document to assure everyone the effective freedom to copy and redistribute it, with or without modifications, either commercially or non-commercially. The latest version is 1.3.

Exceptions to GNU Licenses

Some GNU programs have additional permissions or special exceptions to specific terms in one of the main licenses. Since some of those are commonly used or inspire a lot of questions on their own, we've started collecting them on our exceptions page.

License URLs

When linking to our licenses, it's usually best to link to the latest version; hence the standard URLs such as http://www.gnu.org/licenses/gpl.html have no version number. Occasionally, however, you may want to link to a specific version of a given license. In those situations, you can use the following links [skip links]:

Stable links to each license's alternative formats are available on its respective page. Not every version of every license is available in every format. If you need one that is missing, please email us.

See also the old licenses page.

Unofficial Translations

Legally speaking, the original (English) version of the licenses is what specifies the actual distribution terms for GNU programs and others that use them. But to help people better understand the licenses, we give permission to publish translations into other languages provided that they follow our regulations for unofficial translations:

Verbatim Copying and Distribution

The standard copyright terms for GNU web pages is now the Creative Commons Attribution-NoDerivs 4.0 International License. It used to be (and for a few pages still is):

Verbatim copying and distribution of this entire article are permitted worldwide, without royalty, in any medium, provided this notice is preserved.

Please note the following commentary about this “verbatim license” by Eben Moglen:

“Our intention in using the phrase ‘verbatim copying in any medium’ is not to require retention of page headings and footers or other formatting features. Retention of weblinks in both hyperlinked and non-hyperlinked media (as notes or some other form of printed URL in non-HTML media) is required.”

List of Free Software Licenses

List of Free Software Licenses If you are contemplating writing a new license, please contact the FSF by writing to <licensing@fsf.org>. The proliferation of different free software licenses means increased work for users in understanding the licenses; we may be able to help you find an existing Free Software license that meets your needs. If that isn't possible, if you really need a new license, with our help you can ensure that the license really is a Free Software license and avoid various practical problems.

What Is Copyleft?

Copyleft is a general method for making a program free software and requiring all modified and extended versions of the program to be free software as well.

The simplest way to make a program free is to put it in the public domain, uncopyrighted. This allows people to share the program and their improvements, if they are so minded. But it also allows uncooperative people to convert the program into proprietary software. They can make changes, many or few, and distribute the result as a proprietary product. People who receive the program in that modified form do not have the freedom that the original author gave them; the middleman has stripped it away.

In the GNU project, our aim is to give all users the freedom to redistribute and change GNU software. If middlemen could strip off the freedom, we might have many users, but those users would not have freedom. So instead of putting GNU software in the public domain, we “copyleft” it. Copyleft says that anyone who redistributes the software, with or without changes, must pass along the freedom to further copy and change it. Copyleft guarantees that every user has freedom.

Copyleft also provides an incentive for other programmers to add to free software. Important free programs such as the GNU C++ compiler exist only because of this.

Copyleft also helps programmers who want to contribute improvements to free software get permission to do that. These programmers often work for companies or universities that would do almost anything to get more money. A programmer may want to contribute her changes to the community, but her employer may want to turn the changes into a proprietary software product.

When we explain to the employer that it is illegal to distribute the improved version except as free software, the employer usually decides to release it as free software rather than throw it away.

To copyleft a program, we first state that it is copyrighted; then we add distribution terms, which are a legal instrument that gives everyone the rights to use, modify, and redistribute the program's code or any program derived from it but only if the distribution terms are unchanged. Thus, the code and the freedoms become legally inseparable.

Proprietary software developers use copyright to take away the users' freedom; we use copyright to guarantee their freedom. That's why we reverse the name, changing “copyright” into “copyleft”.

Copyleft is a general concept; there are many ways to fill in the details. In the GNU Project, the specific distribution terms that we use are contained in the GNU General Public License, the GNU Lesser General Public License and the GNU Free Documentation License.

The appropriate license is included in many manuals and in each GNU source code distribution.

The GNU GPL is designed so that you can easily apply it to your own program if you are the copyright holder. You don't have to modify the GNU GPL to do this, just add notices to your program which refer properly to the GNU GPL. Please note that you must use the entire text of the GPL, if you use it. It is an integral whole, and partial copies are not permitted. (Likewise for the LGPL, AGPL, and FDL.)

Using the same distribution terms for many different programs makes it easy to copy code between various different programs. Since they all have the same distribution terms, there is no need to think about whether the terms are compatible. The Lesser GPL includes a provision that lets you alter the distribution terms to the ordinary GPL, so that you can copy code into another program covered by the GPL.

Licenses for Other Types of Works

We believe that published software and documentation should be free software and free documentation. We recommend making all sorts of educational and reference works free also, using free documentation licenses such as the GNU Free Documentation License (GNU FDL).

For essays of opinion and scientific papers, we recommend either the Creative Commons Attribution-NoDerivs 3.0 United States License, or the simple “verbatim copying only” license stated above.

We don't take the position that artistic or entertainment works must be free, but if you want to make one free, we recommend the Free Art License.